Systems, solar articles, and methods comprising a structured protective film

Abstract

A system is described comprising a solar article (110) that comprises a first major surface (that faces the sun during daytime use) and an opposing second major surface. The protective film (150) comprises a first major surface (that faces the sun during daytime use) and an opposing second major surface. The first major surface of the solar article (110) and / or the opposing second major surface of the protective film (150) comprises surface structures (153). The surface structures (153) are microstructures and / or nanostructures having at least two dimensions less than 1 mm. The structures can provide / maintain an air interface (175) between the first major surface of the solar article (110) and the second major surface of the protective film (150). Also described is a structured polyolefin film suitable for use as a protective film (150) for a solar article, as described herein and a method of improving the efficiency of a solar article.

Description

[0001] SYSTEMS, SOLAR ARTICLES, AND METHODS COMPRISING A STRUCTURED PROTECTIVE FILM

[0002] Summary of the Invention

[0003] Passive radiative cooling panels on roofs at various locations have been measured to have soiling factors of 1-2 W / m2 / day resulting in a solar reflectivity decrease from 94% to 89% in 2-3 weeks. Solar reflectivity of less than 90% results in no net radiative cooling at mid-day due to solar absorption in some locations. Thus, passive radiative cooling panels can require cleaning every 2-3 weeks to maintain passive radiative daytime cooling to sub-ambient temperatures at mid-day.

[0004] Photovoltaic modules in dry dusty environments such as Arizona and Dubai can have a decrease in electricity output of 20% due to soiling. In dry dusty locations, photovoltaic modules are often cleaned twice a month to maintain their electricity production.

[0005] The cost of cleaning such solar articles can increase their payback period. For example, passive radiative cooling panels can have a payback period of 4 years, but the cost of cleaning can increase that payback period to 6 years or longer. Payback period for photovoltaic modules can increase from 8 years to 12 years, or even longer, due to the cost of cleaning them.

[0006] Vanous systems have been described concerning utilizing protection films for improving the efficiency of solar power generation (e.g. photovoltaic module). See for example WO2022 / 019735 and CN113364410. Although such systems are concerned with the loss of efficiency caused by dirt, such systems do not take into account the loss of solar transmission caused by the presence of the protection film. Thus, inductry would find advantage in systems, articles, and methods wherin the protection film has (e.g. anti-reflective) structured surfaces.

[0007] In one embodiment, a system is described comprising a solar article and a protection film. The solar article comprises a first major surface (that faces the sun during daytime use) and an opposing second major surface. The protective film comprises a first major surface (that faces the sun during daytime use) and an opposing second major surface. The first major surface of the solar article and / or the opposing second major surface of the protective film comprises surface structures. The surface structures are microstructures and / or nanostructures having at least two dimensions less than 1 mm. The structures can provide / maintain an air interface between the first major surface of the solar article and the second major surface of the protective film.

[0008] In one embodiment, the structured surface can improve the transmission though the protection film into the underlying solar article. With reference to the transmission data report in the forthcoming examples, the protective film has a transmission of at least 95, 96, 97, 98, or 99% for wavelengths ranging from greater than 0.75 microns (750 nm) to 2.5, 2.0, or 3.3 microns (3300 nm). In another embodiment, the protective film has a transmission of at least 95, 96, 97, 98, or 99% at wavelengths ranging from greaterthan 3.6 microns (3600 nm) to 25.0 microns (25000 nm). In another embodiment, the protective film comprises the structures and the protective film has a transmission at least 1, 2, 3, 4, or 5% greater than the same protective film lacking structures for wavelengths ranging from 0.75 microns to 2.5, 3 or 3.3 microns or wavelengths ranging from 3.6 microns to 25.0 microns. In another embodiment, the (e g. polyolefin) protection film can facilitate heat to be radiated to the sky from a surface of a passive radiation cooling panel article.

[0009] In one embodiment, the protective film (e.g. for cooling panel articles) comprises a polyolefin material. The (e.g. cooling panel) solar article may comprise a multilayer film (e.g. that lacks a fluorinated material).

[0010] In one embodiment, the protective film is conveyed across the first major surface of the solar article with a roll to roll apparatus. In some embodiments, the system further comprises an apparatus for cleaning at least the first major surface of the protective film and optionally the opposing major surface. The apparatus for cleaning comprises a pressure sensitive adhesive on a roll. The system may comprise conveying the cleaned protective film across the major surface of the solar article.

[0011] Also described is a structured polyolefin film suitable for use as a protective film for a solar article, as described herein and a method of improving the efficiency of a solar article.

[0012] Brief Description of the Drawings

[0013] FIG. 1A is a cross-sectional view of a solar article comprising a protective film;

[0014] FIG. IB is a magnified view of the interface of a structured protective film with the solar article;

[0015] FIG. 2 is a magnified view of the interface of a protective film with the structured surface of a solar article;

[0016] FIG. 3 is a cross-sectional view of an antireflective structured surface in an xz plane;

[0017] FIG. 4 is top plan view of a protective film mechanically attached to a solar article;

[0018] FIG. 5 is a side view of a protective film being conveyed across the surface of a solar article;

[0019] FIG. 6 is a side view of a protective film being conveyed through a cleaning station and reconveyed across the surface of a solar article;

[0020] Written Description

[0021] Presently described are systems comprising solar articles and a protective film. Representaive solar articles include photovoltaic modules and passive cooling panels.

[0022] FIG. 1A depcits a cross-sectional view of a solar article 110 comprising a protective film 150. The system 100 comprises solar article 110 having a first major surface 111 (that faces the sun during daytime use of the solar article and system) and an opposing second major surface 112. The system 100 further comprises protective film 150 having a first major surface 151 (that faces the sun during daytime use of the solar article and system) and a second major surface 152 proximate the first major surface 111 of the solar article 110.

[0023] FIG. IB is a magnified view of the interface of the second major surface 152 of the protective film 150 with the first major surface 111 of the solar article. The second major surface 152 of the protective film 150 is a structured surface. The second major surface 152 of the protective film 150 comprises structures 153 and an air interface 175 between the first major surface 111 of the solar article 110 and the second major surface 152 of the protective film 150. The structured surface of the protective film is selected such that more light passes through the protective film 150 to the first major surface 111 of the solar article 110.

[0024] FIG 2 is a magnified view of another embodiment wherein the first major surface 111 of the solar article 110 comprises structures 153. In this embodiment, the protective film can be unstructured.

[0025] In another embodiment, (not shown) the second major surface 152 of the protective film 150 comprises structures and the first major surface 111 of the solar article 110 comprises structures 151.

[0026] An air interface 175 is present between the first major surface 111 of the solar article 110 and the second major surface 152 of the protective film 150 because the protective film is proximate, yet not permanently bonded to the solar article. Thus, the protective film is typically not chemically, thermally, or adhesively bonded to the first major surface of the solar article. In another embodiment, it is contemplated that the protective film may be partially bonded to the first major surface of the solar article, yet 50% to 90% or greater of the surface area of the protective film is unbonded. An air interface is present between the unbonded portions of the second surface of the protective film and the first major surface of the solar article. The air interface insulates passive cooling surface 111 of solar article 110 enabling greater sub-ambient cooling to occur by minimizing convective heating by the air above the protective film.

[0027] The protective film may optionally be attached to the first major surface of the solar article by any suitable means does that does not eliminate the air interface between the solar article and protective film, as will subsequently be described in greater detail.

[0028] Protective Film

[0029] In general, the protective film is positioned between the outer (e.g. first major) surface of the solar article and at least one source of solar energy (e.g., the sun). The protective film may partially, but more typically fully covers the first major surface of the solar article.

[0030] The protective film is typically exposed to elements of an outdoor environment, especially dirt. The protection film comprises a material suitable for an outdoor environment for the intended amount of time the protection film will be used. The intended amount of time of use is typically less than 1 month for protection films that will be replaced when soiled. However, for protection films that are cleaned and reused, the intended amount of time of use may be 6 months, 1 year, or greater.

[0031] The protective film is formed of a material that provides high transmission of solar energy and thus solar energy can be transmitted through the protection film. One class of materials that has suitable low absorption and high transmission of solar energy is polyolefins. Polyolefins (e.g. polyethylene) is also transparent in the mid-infrared wavelengths of 8-13 microns which facilitates heat to be radiated to the sky from a surface of the passive radiation cooling panel article below the polyolefin (e.g. polyethylene) film.

[0032] Illustrative polyolefin materials include low density polyethylene, such as available from DOW Corporation as DOW 9551, DOWLEX 2047G linear low density polyethylene also available from DOW Corporation as DOWLEX 2047G, medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). Polyolefin copolymers including polymethylpentene (PMP), poly (ethylene-co-octene) (PE-PO) (e.g., available under the trade designation “ENGAGE 8200” from Dow Elastomers, Midland, MI), poly (propylene-co-ethylene) (PPPE) (e.g., available under the trade designation “Z9470” from Atofina Petrochemicals, Inc., Houston, TX); polypropylene copolymers such as copolymers of atactic polypropylene (aPP) and isotactic polypropylene (iPP); cyclic olefin polymer (COP); and cyclic olefin copolymer (COC). In some embodiments, the cyclic olefin copolymer is a copolymer of norbomene and ethylene, such as available under the tradename Zeonor from Zeon Corporation.

[0033] In some embodiments, the (e g. polyethylene) polyolefin material has a density (ASTM D792) of at least 0.90, 0.91, or 0.92 and less than 0.93 g / cc. In some embodiments, the (e.g. polyethylene) polyolefin material has a melt index (190°C / 2.16 kg - ASTM D1238) of at least 10, 15, 20, 25, or 30 g / lOmin and no greater than 40, 45, or 50 g / 10 min. In some embodiments, the (e.g. polyethylene) polyolefin material has a tensile strength (ASTM D638) at break of at least 5, 6, or 7 MPa and no greater than lOMPa. In some embodiments, the (e.g. polyethylene) polyolefin material has an elongation (ASTM D638) at break of at least 50, 75 or 100% and no greater than 150%.

[0034] When the solar article is a photovoltaic module, the transparency in the mid-infrared wavelengths, is of less importance. Thus other film materials that have a high transmission of (e.g. visible light) solar energy can be utilized such as acrylic (PMMA), acrylonitrile butadiene styrene (ABS), cellulose acetate, polystyrene (PS), polyvinyl chloride (PVC), polyesters including polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETg), polycyclohexylenedimethylene terephthalate (PCT), polycyclohexylenedimethylene terephthalate glycol (PCTg), poly(l,4 cyclohexylenedim ethylene) terephthalate (PCT ); polycarbonate (PC), polyamides including nylons, polyetherimide (PEI), polyphenylene sulphide (PPS), and fluoropolymers.

[0035] In some embodiments, the protective film is a thermoplastic film that is amenable to recycling the soiled protective film or preparing the protective film from recycled materials. The melt or softening temperature is a physical property of a thermoplastic As used herein the term thermal melt or softening transition temperature refers to the Vicat Softening Temperature measured according to ASTM DI 525 - 17 of an (e.g. amorphous) thermoplastic polymer or the melt temperature (Tm) of a thermoplastic polymer having crystallinity as measured by differential scanning calorimeter according to ASTM D3418.

[0036] In some embodiments, the protective film has athermal melt (DSC) or Vicat softening temperature (ASTM1525) of at least 50, 55, 60, 65, 70, 75, or 80°C. The thermal melt or softening temperature is typically no greater than 450, 425, 400, 375, 350, 325, 300, 275, 250, 200, or 175°C. In some embodiments, the thermal melt or softening temperature (e.g. of the polyolefin) protective film is no greaterthan 180, 170, 165, 160, 155, 150, 145, 140, 135, 130, 125 or 120°C.

[0037] Structured Surface

[0038] With reference to FIGS. 1A and IB, the protective film comprises structures on at least the second major surface 152 proximate the first major surface 111 of the solar article and / or the first major surface of the solar article comprises structures. The structures 151 structures have at least two dimensions less than 1 mm. In some embodiments, the structures may be characterized as microstructures. As used herein microstructures refers to structures having at least two dimensions, e.g. width and height, or all three dimension, i.e. width, height, and length (largest dimension) of at least 1 micron and less than 1 mm. In some embodiment, the maximum dimension of the microstructures is no greater than 900, 800, 700, 600, 500, 400, 300, 200, or 100 microns. In some embodiments, the minimum dimension of the microstructures (e.g. peak width and / or peak height) is at least 2, 3, 4, 5, 6, 7, 8, 9, or 10 microns. In some embodiments, the minimum dimension of the microstructures (e.g. width and / or height) is at least 15, 20, 25, 30, 35, 40, 45, or 50 microns.

[0039] In other embodiments, the structures may be characterized as nanostructures. As used herein nanostructures refers to structures having at least one or two dimensions less than 1 micron. In some embodiments, the minimum dimension of the nanostructures (e.g. peak height) is at least 10, 50, 75, 100, 120, 140, 150, 160, 180, 200, 250 or 500 nm. In some embodiments, the nanostructures have a peak height that ranges from 100 to 250 nm. In some embodiments, the nanostructures have a peak height that ranges from 75 to 160 nm.

[0040] Various structured surfaces are known in the literature. The base of each (e g. micro)structure may comprise various cross-sectional shapes including but not limited to parallelograms with optionally rounded comers, rectangles, squares, circles, half-circles, half-ellipses, triangles trapezoids, other polygons (e.g. pentagons, hexagons, octagons, etc. and combinations thereof. In some embodiments, the peak structures may be described as posts, domes, ribs, prisms, or cube-comer elements.

[0041] In some embodiments, the stmetured surface of the protection film comprises microstructures and nanostructures. In some embodiments, the stmetured surface of the protection film comprises microstructures that further comprise nanostructures. The average distance between the microstructure peaks is typically at least 10 times the average distance between the nanostructure peaks.

[0042] Various types of structures can increase the solar transmission. In some embodiments, the stmetured surface may be described as a matte stmetured surface, an antiglare stmetured surface, or more preferably as antireflective stmetured surface.

[0043] Matte and antiglare stmetured surface may be characterized according to surface roughness criteria. The average surface roughness (i.e. Ra) is typically less than 0.20 microns. The favored embodiments having high clarity in combination with sufficient haze exhibit a Ra of less no greater than 0 18 or 0.17 or 0.16 or 0.15 microns. In some embodiments, the Ra is less than 0.14, or 0.13, or 0.12, or 0.11, or 0.10 microns. The Ra is typically at least 0.04 or 0.05 microns.

[0044] In some embodiments, microstructures of the matte film typically have a height distribution. In some embodiments, the mean height is not greater than about 5, 4, 3, 2, or 1 micron. The mean height is typically at least 0.1, 0.2, 0.3, 0.5, or 0.5 microns.

[0045] The roughness can be determined as described in W02010 / 141345; incorporated herein by reference. Suitable microstmctured matte layers can be formed from replication of a tool. Advantageously such technique does not necessitate the use of matte (e.g. inorganic) particles that typically reduce solar transmission.

[0046] In favored embodiments, the structured surface of the second major surface of the protection film and / or first major surface of the solar article may be characterized as antireflective.

[0047] According to the literature, antireflective films can be made by other methods, such as coatings with matte particles or by providing high and low refractive index layers on a substrate. However, such methods can introduce other materials (e.g. inorganic particles) that typically absorb or reflect wavelengths of solar radiation. Hence, an overall improvement in transmission of solar wavelengths of light is typically not achieved.

[0048] Various (e.g. antireflective) structured surfaces comprising microstructures and / or nanostructures and methods of making such structured surfaces are known. See for example W02019 / 130198; incorporated herein by reference.

[0049] FIG. 3 shows an embodied antireflective surface 202 of layer 208 with nanostructures 330, 332, (which are visible in two magnified overlays) disposed on the surface of microstructures (also referred to as micro-peaks). The structured surface comprises nanostructures on the peaks of (e.g. linear prim) microstructures and nanostructures on the unstructured surface (e.g. land layer, flat lanes) between microstructures. At least one micro-peak 220 may include at least one first micro-segment 224 or at least one second micro-segment 226. Micro-segments 224, 226 may be disposed on opposite sides of apex 248 of micro-peak 220. Apex 248 may be, for example, the highest point or local maxima of line 214. Each micro-segment 224, 226 may include at least one: straight segment or curved segment.

[0050] Line 214 defining first and second micro-segments 224, 226 may have a first average slope and a second average slope, respectively. The slopes may be defined relative to baseline 250 as an x-axis (run), wherein an orthogonal direction is the z-axis (rise).

[0051] As used herein, the term “average slope” refers to an average slope throughout a particular portion of a line. In some embodiments, the average slope of first micro-segment 224 may refer to the slope between the endpoints of the first micro-segment. In some embodiments, the average slope of first micro-segment 224 may refer to an average value calculated from the slopes measured at multiple points along the first micro-segment.

[0052] In general, the micro-peak first average slope may be defined as positive and the micro-peak second average slope may be defined as negative. In other words, the first average slope and the second average slope have opposite signs. In some embodiments, the absolute value of the micro-peak first average slope may be equal to the absolute value of the micro-peak second average slope. In some embodiments, the absolute values may be different. In some embodiments, the absolute value of each average slope of microsegments 224, 226 may be greater than the absolute value of the average slope of micro-space 222.

[0053] Angle A of micro-peaks 220 may be defined between the micro-peak first and second average slopes. In other words, the first and second average slopes may be calculated and then an angle between those calculated lines may be determined. For purposes of illustration, angle A is shown as relating to first and second micro-segments 224, 226. In some embodiments, however, when the first and second micro- segments are not straight lines, the angle A may not necessarily be equal to the angle between two microsegments 224, 226.

[0054] Angle A may be in a range to provide sufficient anti-reflective properties for surface 202 In some embodiments, angle A may be at most 120 (in some embodiments, at most 110, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or even at most 10) degrees. In some embodiments, angle A is at most 85 (in some embodiments, at most 75) degrees. In some embodiments, angle A is, at the low end, at least 30 (in some embodiments, at least 25, 40, 45, or even at least 50) degrees. In some embodiments, angle A is, at the high end, at most 75 (in some embodiments, at most 60, or even at most 55) degrees.

[0055] Micro-peaks 220 may be any suitable shape capable of providing angle A based on the average slopes of micro-segments 224, 226. In some embodiments, micro-peaks 220 are generally formed in the shape of a triangle. In some embodiments, micro-peaks 220 are not in the shape of a triangle. The shape may be symmetrical across a z-axis intersecting apex 248. In some embodiments, the shape may be asymmetrical.

[0056] Each micro-space 222 may define micro-space width 242. Micro-space width 242 may be defined as a distance between corresponding boundaries 216, which may be between adjacent micro-peaks 220.

[0057] A minimum for micro-space width 242 may be defined in terms of micrometers. In some embodiments, micro-space width 242 may be at least 10 (in some embodiments, at least 20, 25, 30, 40, 50, 60, 70, 75, 80, 90, 100, 150, 200, or even at least 250) micrometers. In some applications, micro-space width 242 is, at the low end, at least 50 (in some embodiments, at least 60) micrometers. In some applications, micro-space width 242 is, at the high end, at most 90 (in some embodiments, at most 80) micrometers. In some applications, micro-space width 242 is 70 micrometers.

[0058] As used herein, the term “peak distance” refers to the distance between consecutive peaks, or between the closest pair of peaks, measured at each apex or highest point of the peak.

[0059] Micro-space width 242 may also be defined relative to micro-peak distance 240. In particular, a minimum for micro-space width 242 may be defined relative to corresponding micro-peak distance 240, which may refer to the distance between the closest pair of micro-peaks 220 surrounding micro-space 222 measured at each apex 248 of the micro-peaks. In some embodiments, micro-space width 242 may be at least 10% (in some embodiments, at least 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, or even at least 90%) of the maximum for micro-peak distance 240. In some embodiments, the minimum for micro-space width 242 is, at the low end, at least 30% (in some embodiments, at least 40%) of the maximum for micropeak distance 240. In some embodiments, the minimum for micro-space width 242 is, at the high end, at most 60% (in some embodiments, at most 50%) of the maximum for micro-peak distance 240. In some embodiments, micro-space width 242 is 45% of micro-peak distance 240.

[0060] A minimum the micro-peak distance 240 may be defined in terms of micrometers. In some embodiments, micro-peak distance 240 may be at least 1 (in some embodiments, at least 2, 3, 4, 5, 10, 25, 50, 75, 100, 150, 200, 250, or even at least 500) micrometers. In some embodiments, micro-peak distance 240 is at least 100 micrometers. A maximum for micro-peak distance 240 may be defined in terms of micrometers. Micro-peak distance 240 may be at most 1000 (in some embodiments, at most 900, 800, 700, 600, 500, 400, 300, 250, 200, 150, 100, or even at most 50) micrometers. In some embodiments, micro-peak distance 240 is, at the high end, at most 200 micrometers. In some embodiments, micro-peak distance 240 is, at the low end, at least 100 micrometers. In some embodiments, micro-peak distance 240 is 150 micrometers.

[0061] Each micro-peak 220 may define micro-peak height 246. Micro-peak height 246 may be defined as a distance between baseline 350 and apex 248 of micro-peak 220. A minimum may be defined for micropeak height 246 in terms of micrometers. In some embodiments, micro-peak height 246 may be at least 10 (in some embodiments, at least 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, or even at least 250) micrometers. In some embodiments, micro-peak height 246 is at least 60 (in some embodiments, at least 70) micrometers. In some embodiments, micro-peak height 246 is 80 micrometers.

[0062] Plurality of nanostructures 330, 332 may be defined at least partially by line 214. Plurality of nanostructures 330 may be disposed on at least one or micro-space 222. In particular, line 314 defining nanostructures 330 may include at least one series of nano-peaks 320 disposed on at least one micro-space 222. In some embodiments, at least one series of nano-peaks 320 of plurality of nanostructures 332 may also be disposed on at least one micro-peak 220.

[0063] Due to at least their difference in size, microstructures 218 may be more durable than nanostructures 330, 332 in terms of abrasion resistance. In some embodiments, plurality of nanostructures 332 are disposed only on micro-spaces 222 or at least not disposed proximate to or adjacent to apex 248 of micro-peaks 220.

[0064] Each nano-peak 320 may include at least one of first nano-segment 324 and second nano-segment 326. Each nano-peak 320 may include both nano-segments 324, 326. Nano-segments 324, 326 may be disposed on opposite sides of apex 348 of nano-peak 320.

[0065] First and second nano-segments 324, 326 may define a first average slope and a second average slope, respectively, which describe line 314 defining the nano-segment. For nanostructures 330, 332, the slope of line 314 may be defined relative to baseline 350 as an x-axis (run), wherein an orthogonal direction is the z-axis (rise).

[0066] In general, the nano-peak first average slope may be defined as positive and the nano-peak second average slope may be defined as negative, or vice versa. In other words, the first average slope and the second average slope at least have opposite signs. In some embodiments, the absolute value of the nanopeak first average slope may be equal to the absolute value of the nano-peak second average slope (e.g., nanostructures 330). In some embodiments, the absolute values may be different (e.g., nanostructures 332).

[0067] Angle B of nano-peaks 320 may be defined between lines defined by the nano-peak first and second average slopes. Similar to angle A, angle B as shown is for purposes of illustration and may not necessarily equal to any directly measured angle between nano-segments 324, 326.

[0068] Angle B may be a range to provide sufficient anti-reflective properties for surface 202. In some embodiments, angle B may be at most 120 (in some embodiments, at most 110, 100, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or even at most 10) degrees. In some embodiments, angle B is, at the high end, at most 85 (in some embodiments, at most 80, or even at most 75) degrees In some embodiments, angle B is, at the low end, at least 55 (in some embodiments, at least 60, or even at least 65) degrees. In some embodiments, angle B is 70 degrees.

[0069] Angle B may be the same or different for each nano-peak 320. For example, in some embodiments, angle B for nano-peaks 320 on micro-peaks 220 may be different than angle B for nano-peaks 320 on micro-spaces 222.

[0070] Nano-peaks 320 may be any suitable shape capable of providing angle B based on lines defined by the average slopes of nano-segments 324, 326. In some embodiments, nano-peaks 320 are generally formed in the shape of a triangle. In at least one embodiments, nano-peaks 320 are not in the shape of a triangle. The shape may be symmetrical across apex 348. For example, nano-peaks 320 of nanostructures 330 disposed on micro-spaces 222 may be symmetrical. In at least one embodiments, the shape may be asymmetrical. For example, nano-peaks 320 of nanostructures 332 disposed on micro-peaks 220 may be asymmetrical with one nano-segment 324 being longer than other nano-segment 326. In some embodiments, nano-peaks 320 may be formed with no undercutting.

[0071] Each nano-peak 320 may define nano-peak height 346. Nano-peak height 346 may be defined as a distance between baseline 350 and apex 348 of nano-peak 320. A minimum may be defined for nano-peak height 346 in terms of nanometers. In some embodiments, nano-peak height 346 may be at least 10 (in some embodiments, at least 50, 75, 100, 120, 140, 150, 160, 180, 200, 250, or even at least 500) nanometers.

[0072] In some embodiments, nano-peak height 346 is at most 250 (in some embodiments, at most 200) nanometers, particularly for nanostructures 330 on micro-spaces 222. In some embodiments, nano-peak height 346 is in a range from 100 to 250 (in some embodiments, 160 to 200) nanometers. In some embodiments, nano-peak height 346 is 180 nanometers.

[0073] In some embodiments, nano-peak height 346 is at most 160 (in some embodiments, at most 140) nanometers, particularly for nanostructures 332 on micro-peaks 220. In some embodiments, nano-peak height 346 is in a range from 75 to 160 (in some embodiments, 100 to 140) nanometers. In some embodiments, nano-peak height 346 is 120 nanometers.

[0074] As used herein, the terms “corresponding micro-peak” or “corresponding micro-peaks” refer to micro-peak 220 upon which nano-peak 320 is disposed or, if the nano-peak is disposed on corresponding micro-space 222, refers to one or both of the closest micro-peaks that surround that micro-space. In other words, micro-peaks 220 that correspond to micro-space 222 refer to the micro-peaks in the series of micropeaks that precede and succeed the micro-space.

[0075] Nano-peak height 346 may also be defined relative to micro-peak height 246 of corresponding micro-peak 220. In some embodiments, corresponding micro-peak height 246 may be at least 10 (in some embodiments, at least 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, or even at least 1000) times nano-peak height 346. In some embodiments, corresponding micro-peak height 246 is, at the low end, at least 300 (in some embodiments, at least 400, 500, or even at least 600) times nano-peak height 346. In some embodiments, corresponding micro-peak height 246 is, at the high end, at most 900 (in some embodiments, at most 800, or even at most 700) times nano-peak height 346. Nano-peak distance 340 may be defined between nano-peaks 320. A maximum for nano-peak distance 340 may be defined. In some embodiments, nano-peak distance 340 may be at most 1000 (in some embodiments, at most 750, 700, 600, 500, 400, 300, 250, 200, 150, or even at most 100) nanometers. In some embodiments, nano-peak distance 340 is at most 400 (in some embodiments, at most 300) nanometers.

[0076] A minimum for the nano-peak distance 340 may be defined. In some embodiments, nano-peak distance 340 may be at least 1 (in some embodiments, at least 5, 10, 25, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, or even at least 500) nanometers. In some embodiments, nano-peak distance 340 is at least 150 (in some embodiments, at least 200) nanometers.

[0077] In some embodiments, the nano-peak distance 340 is in a range from 150 to 400 (in some embodiments, 200 to 300) nanometers. In some embodiments, the nano-peak distance 340 is 250 nanometers.

[0078] Nano-peak distance 340 may be defined relative to the micro-peak distance 240 between corresponding micro-peaks 220. In some embodiments, corresponding micro-peak distance 240 is at least 10 (in some embodiments, at least 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, or even at least 1000) times nano-peak distance 340. In some embodiments, corresponding micro-peak distance 240 is, at the low end, at least 200 (in some embodiments, at least 300) times nano-peak distance 340. In some embodiments, corresponding micro-peak distance 240 is, at the high end, at most 500 (in some embodiments, at most 400) times the nano-peak distance 340.

[0079] In some embodiments of forming anti-reflective surface 202 of layer 208, a method may include extruding a thermoplastic (e.g. polyolefin) material. The extruded material may be shaped with a microreplication tool. The micro-replication tool may include a mirror image of a series of micro-structures, which may form the series of micro-structures on the surface of the layer 208. The series of micro-structures may include a series of alternating micro-peaks and micro-spaces along an axis. A plurality of nanostructures may be formed on the surface of the layer on at least the micro-spaces. The plurality of nanopeaks may include at least one series of nano-peaks along the axis.

[0080] In some embodiments, the plurality nanostructures may be formed by exposing the surface to reactive ion etching. For example, masking elements may be used to define the nano-peaks.

[0081] In some embodiments, the plurality of nanostructures may be formed by shaping the extruded material with the micro-replication tool further having an ion-etched diamond. This method may involve providing a diamond tool wherein at least a portion of the tool comprises a plurality of tips, wherein the pitch of the tips may be less than 1 micrometer, and cutting a substrate with the diamond tool, wherein the diamond tool may be moved in and out along a direction at a pitch (pi). The diamond tool may have a maximum cutter width (p ) and — > 2.

[0082] P2

[0083] The nanostructures may be characterized as being embedded within the microstructured surface of the layer 208. Except for the portion of the nanostructure exposed to air, the shape of the nano-structure may generally be defined by the adjacent micro-structured material. In some embodiments, the plurality of nanostructures may be formed by shaping the extruded material, or layer 208, with the micro-replication tool further having a nano-structured granular plating for embossing. Electrodeposition, or more specifically electrochemical deposition, can also be used to generate various surface structures including nanostructures to form a micro-replication tool. The tool may be made using a 2-part electroplating process, wherein a first electroplating procedure may form a first metal layer with a first major surface, and a second electroplating procedure may form a second metal layer on the first metal layer. The second metal layer may have a second major surface with a smaller average roughness than that of the first major surface. The second major surface can function as the structured surface of the tool. A replica of this surface can then be made in a major surface of an optical film to provide light diffusing properties. One example of an electrochemical deposition technique is described in U.S. Pat. Appl. Having U.S. Serial No. 62 / 446821, PCT Pub. No. WO 2018 / 130926, published July 19, 2018 (Derks et al.), filed 16 January 2017, entitled “Faceted Micro-structured Surface,” the disclosures of which are incorporated entirely herein by reference.

[0084] The protective film 150 may optionally comprises structures on the first major surface 151 that faces the sun during daytime use of the solar article. The optional structures of the first major surface 151 of protective film 150 may be described as antireflective, antiglare, or matte surface.

[0085] In some embodiments, the optional structured surface of the first major surface of the protective film may prevent microorganisms (e.g. bacteria such as Streptococcus mutans, Staphyloccus aureus, or Psueodomonas aeruginosa) from being present on the structured surface or in other words reduces or prevents biofilm from forming. Various structured surfaces have been described in the literature including US2017 / 0100332, W02013 / 003373, and WO 2012 / 058605; incorporated herein by reference.

[0086] In some embodiments, the structured surface of the film may be chosen to provide one or more or the following properties: i) a reduction in microorganism touch transfer of at least 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, or 99%; ii) a log 10 reduction of microorganism (e.g. bacteria) of at least 2, 3, 4, 5, 6, 7 or 8 after cleaning; iii) at least 50, 60, 70, 80, 90% of the structured surface comprising cleaning solution 1-3 minutes after applying the cleaning solution to the (e.g. micro)structured surface. Structured surfaces of this type are described in WO2022 / 162528; incorporated herein by reference.

[0087] In this embodiments, the microstructures typically have a side wall angle greater than 10, 15, 20, 25, 30, 35, 40, or 45 degrees.

[0088] In some embodiments, the structured surface comprises microstructures wherein the maximum or average width of the valleys (e.g. 240 of of FIG. 3) is at least 1, 2, 3, or 4 microns and more typically greater than 5, 6, 7, 8, 9, or 10 microns ranging up to 250 microns. In some embodiments, the width of the valleys is at least 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 microns. In some embodiments, the width of the valleys is at least 30, 35, 40, 45, or 50 microns. In some embodiments, the width of the valleys is at least 50, 55, 60, 65, 70, 75, 85, 85, 90, 95 or 100 microns. In some embodiments, the width of the valleys is at least 125, 150, 175, 200, 225, or 250 microns. In some embodiments, the width of the valleys is no greater than 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 225, 200, 175, 150, 125, 100, 75, or 50 microns. In some embodiments, the maximum or average width of the peaks (i.e. 244 of FIG. 3) is about the same as the valleys. In other embodiments, the peak width is not the same as the valley width, yet may fall within the same ranges just described for the valleys.

[0089] The height of the peaks is typically within the same range as the maximum width of the valleys as previously described. In some embodiments, the peak structures typically have a height (H) ranging from 1 to 125 microns. In some embodiments, the height of the microstructures is at least 2, 3, 4, or 5 microns. In some embodiments, the height of the microstructures is at least 6, 7, 8, 9 or 10 microns. In some embodiments, the height of the microstructures no greater than 100, 90, 80, 70, 60, or 50 microns. In some embodiments, the height of the microstructures is no greater than 45, 40, 35, 30 or 25 microns. In some embodiments, the height of the microstructures is no greater than 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, or 10 microns. In typical embodiments, the height of the valley or channel is within the same range as just described for the peak structures. In some embodiments, the peak structures and valleys have the same height. In other embodiments, the peak structures can vary in height.

[0090] The aspect ratio of the valley is the height of the valley (which can be the same as the peak height of the structure) divided by the maximum width of the valley. In some embodiment the aspect ratio of the valley is at least 0.1, 0.15, 0.2, or 0.25. In some embodiments, the aspect ratio of the valley is no greater than 1, 0.9, 0.8, 0.7, 0.6 or 0.5. Thus, in some embodiments, the height of the valley is typically no greater than the maximum width of the valley, and more typically less than the maximum width of the valley.

[0091] In some embodiments, the peak structures comprise two or more facets. The peak structures have an apex that is sharp, rounded or truncated. The peak structures may have an apex angle ranging from 20 to 120 degrees or 80 to 100 degrees. In some embodiments, the (e.g. micro) structured surface comprises less than 50, 40, 30, 20 or 10% of flat surface area that is parallel to the planar base layer. In some embodiments, the facets may form continuous or semi-continuous surfaces in the same direction. In some embodiments, the valleys lack intersecting walls.

[0092] Solar Articles

[0093] The system is useful for various solar articles. The term “solar articles” refer to articles wherein their primary purpose is to convert solar energy (e.g. on earth) or articles that reflect solar energy to minimize solar absorption to enable passive cooling articles.

[0094] In some embodiments, the solar article converts solar energy into electrical energy, such as in the case of photovoltaic modules.

[0095] In other embodiments, the solar article may form part of a cooling panel that may be disposed on the extenor of at least part of a building. Cooling panels reflect sunlight to prevent the panels from heating up during the day. In some embodiments, cooling panels also emits infrared heat to the cold sky (e.g. at night), which cools the panels as well as any fluid flowing in them cool.

[0096] Cooling articles can be applied to a substrate, or object, to reflect light in a solar region of the electromagnetic spectrum and radiate light in an atmospheric window region of the electromagnetic spectrum, both of which may cool the substrate. Although reference is made herein to certain applications, the passive cooling article may be used in any outdoor environment to cool a structure, particularly structures exposed to sunlight. Non-limiting examples of applications of the passive cooling article include commercial building air conditioning, commercial refrigeration (e.g., supermarket refrigerators), heat transfer panels that cool fluids which can be coupled to air conditioning and refrigeration systems, data center cooling of heat transfer fluid systems, power generator cooling, or vehicle air conditioning or refrigeration (e.g., cars, trucks, trains, buses, ships, airplanes, etc ), outdoor electrical transformers, outdoor electrical switch boxes, or cooling of electric vehicle batteries. Passive cooling articles can be integrated with air conditioning and refrigeration systems and depending on the climate can be used to replace an air conditioning unit. In some embodiments, passive cooling articles can replace the refrigerant condensers in air conditioning and refrigeration systems.

[0097] Cooling articles can utilize layers of materials selected to provide specific reflectivity and emission properties. The amount of cooling and temperature reduction may depend on the reflective and absorptive properties of article.

[0098] In some embodiments, the (e g. passive) cooling article solar article reflects at least 90% of light of wavelength of 300 nm to 2500 nm.

[0099] In some embodiments, the (e g. passive) cooling article comprises a surface coating that comprises solar reflective pigments and microspheres, such as described in US 7503971. In some embodiments, the surface of the (e.g. passive) radiative cooling article may comprise at least one of ZnO, Si, HfD2, or ZnO2, as described in US11359841. Such (e.g. passive) cooling articles are commercially available from SkyCool Systems.

[0100] In some embodiments, the (e g. passive) cooling articles comprise a multilayer optical film as a solar reflector. The multilayer optical film can be thin to facilitate heat transfer. In some embodiments, the total thickness of the multilayer film is no greater than 50, 40, 30, 25, 20, 15, or 10 micrometers. The multilayer film comprises layer has up to 1000, 1500 or 2000 2000 (in some embodiments, up to 700, 600, 500, 400, 300, 250, 200, 150, or even up to 100).

[0101] The refractive indices of adjacent optical layers may be different. First optical layer may be described as a low index layer and second optical layer may be described as a high index layer, or vice versa.

[0102] Exemplary polymers useful for forming the high refractive index optical layers include polyethylene terephthalate (PET), available from 3M Company, and also available from Nan Ya Plastics Corporation, Wharton, TX. Copolymers of PET including PETG and PCTG under the trade designation “SPECTAR 14471” and “EASTAR GN071” from Eastman Chemical Company, Kingsport, TN, are also useful high refractive index layers. The molecular orientation of PET and CoPET may be increased by stretching which increases its in-plane refractive indices providing even more reflectivity in the multilayer optical fdm.

[0103] Exemplary isotropic optical polymers, especially for use in the low refractive index optical layers, may include homopolymers of polymethylmethacrylate (PMMA), such as those available from Ineos Acrylics, Inc., Wilmington, DE, under the trade designations “CP71” and “CP80;” and polyethyl methacrylate (PEMA), which has a lower glass transition temperature than PMMA. Additional useful polymers include copolymers of PMMA (CoPMMA), such as a CoPMMA made from 75 wt.% methylmethacrylate (MMA) monomers and 25 wt.% ethyl acrylate (EA) monomers, (e.g., available under the trade designation “PERSPEX CP63” from Ineos Acrylics, Inc., or available under the trade designation “ATOGLAS 510” from Arkema, Philadelphia, PA), a CoPMMA formed with MMA comonomer units and n-butyl methacrylate (nBMA) comonomer units, or a blend of PMMA and poly(vinylidene fluoride) (PVDF). Additional exemplary optical polymers include acrylate triblock copolymers, where each endblock of at least one of the first block copolymer, the second block copolymer, or the at least one additional block copolymer is comprised of poly(methyl methacrylate), and further wherein each midblock of at least one of the first block copolymer or the second block copolymer is comprised of poly(butyl acrylate). In some exemplary embodiments, at least one of the first block copolymer, the second block copolymer, or the at least one additional block copolymer is comprised of from 30 wt.% to 80 wt.% endblocks, and from 20 wt.% to 70 wt.% midblocks, based on a total weight of the respective block copolymer. In certain particular exemplary embodiments, at least one of the first block copolymer, the second block copolymer, or the at least one additional block copolymer is comprised of from 50 wt.% to 70 wt.% endblocks, and from 30 wt.% to 50 wt.% midblocks, based on the total weight of the respective block copolymer. In any of the foregoing exemplary embodiments, the first block copolymer may be selected to be the same as the second block copolymer. Triblock acrylate copolymers are available, for example, under the trade designation “KURARITY LA4285” from Kuraray America, Inc., Houston, TX.

[0104] Additional suitable polymers for use in the low refractive index optical layers, may include polyolefin copolymers, as previously described for the protection film. The multilayer optical films can also include, functionalized polyolefin, such as linear low-density polyethylene -graft-maleic anhydride (LLDPE-g-MA) (e.g., available underthe trade designation “BYNEL 4105” from E.I. du Pont de Nemours & Co., Inc., Wilmington, DE).

[0105] Multilayer optical films described herein can be made using general processing techniques, such as those described in U.S. Pat. No. 6,783,349 (Neavin et al.), which is incorporated entirely herein by reference.

[0106] In one embodiment, the multilayer optical film may comprise first optical layer that comprise a fluoropolymer and second optical layers that comprise a polyester, such as polyethylene terephthalate, as described in W02019 / 130199; incorporated herein by reference. In other embodiments, the multilayer optical film comprises first optical layers that comprise non-fluorinated low refractive index optical layers as described herein such as a CoPMMA.

[0107] In some embodiments, the multilayer optical film may include a metallic layer. Non-limiting examples of metals used in the metallic layer include at least one of: silver (Ag), copper (Cu), aluminum (Al), gold (Au), Inconel, stainless steel, or various combinations thereof. In some embodiments, metallic layer comprises a 100-nanometer thick layer of silver and a 20-nanometer thick layer of copper to protect the silver from corrosion.

[0108] In some embodiments, the multilayer fdm is highly reflective at a lower wavelength range and the metallic layer is highly reflective in a higher wavelength range. In one embodiment, the multilayer film is highly reflective in a range from 0.35 to 0.8 micrometer. In one embodiment, the metallic layer is highly reflective in a range from 0.8 to 2.5 micrometers. Together, the multilayer film and metallic layer provide high reflectivity in a range from 0.35 to 2.5 micrometers.

[0109] In some emboidments, the multilayer film may include inorganic particles. When the (e.g. passive) cooling article comprises a structured surface, the stuctures may include inorganic particles, For example, each structure depicted may correspond to one inorganic particle. The inorganic particles may be dispersed in or disposed on at least one layer. The inorganic particles may comprise titania, silica, zirconia, or zinc oxide. The inorganic particles may be in the form of nanoparticles including nanotitania, nanosilica, nanozironia, or even nano-scale zinc oxide particles. The inorganic particles may be in the form of beads or microbeads. The inorganic particles may be formed of a ceramic material, glass, or various combinations of thereof. In some embodiments, the inorganic particles have an effective D90 particle size of at least 1 (in some embodiments, at least 3, 5, 6, 7, 8, 9, 10, or even at least 13) micrometers. In some embodiments, the inorganic particles have an effective D90 particle size of at most 40 (in some embodiments, at most 25, 20, 15, 14, 13, 12, 11, 10, 9, or even at most 8) micrometers.

[0110] In some embodiments, the cooling film may be characterized as a composite cooling film. Illustrative composite cooing films that comprise a microporous layer are described in US 116346131 incorporated herein by references. Such microporous layer may comprise a micro-voided film.

[0111] The reflective microporous layer may comprise a network of interconnected voids and / or discrete voids, which may be spherical, oblate, or some other shape . Primary functions of the reflective microporous layer include reflecting at least a portion of visible and infrared radiation of the solar spectrum and to emit thermal radiation in the atmospheric window (i.e., wavelengths of 8 to 14 microns).

[0112] Accordingly, the reflective microporous layer has voids that are of appropriate size that they diffusely reflect wavelengths in the 400 to 2500 nm wavelength range. Generally, this means that the void sizes should be in a size range (e.g., 100 to 3000 nm). Preferably, a range of void sizes corresponding to those dimensions is present so that effective broadband reflection will be achieved. As used herein the term "polymer" includes synthetic and natural organic polymers (e g , cellulose and its derivatives).

[0113] Reflectivity of the reflective microporous layer is generally a function of the number of polymer film / void interfaces, since reflection (typically diffuse reflection) occurs at those locations. Accordingly, the porosity and thickness of the reflective microporous layer will be important variable. In general, higher porosity and higher thickness correlate with higher reflectivity. However, for cost considerations film thickness is preferably minimized, although this is not a requirement. Accordingly, the thickness of the reflective microporous layer is typically in the range of 10 microns to 500 microns, preferably in the range of 10 microns to 200 microns, although this is not a requirement. Likewise, the porosity of the reflective microporous layer is typically in the range of 10 volume percent to 90 volume percent, preferably in the range of 20 volume percent to 85 volume percent, although this is not a requirement.

[0114] The use of a reflective micro-voided polymer film as the reflective microporous layer may provide a reflectance that is even greater than that of a silvered mirror. In some embodiments, a reflective micro-voided polymer film reflects a maximum amount of solar energy in a range from 400 to 2500 nanometers (nm). In particular, the use of a fluoropolymer blended into the micro-voided polymer film may provide a reflectance that is greater than other conventional multilayer optical films. Further, inorganic particles including barium sulfate, calcium carbonate, silica, alumina, aluminum silicate, zirconia, and titania may be blended into the micro-voided polymer film for providing high solar reflectance in solar radiation spectra of 0.4 to 2.5 microns and high absorbance in the atmospheric window of 8 to 13 microns.

[0115] In other embodiments, the composite (e.g. passive) cooling film may comprise reflective nonporous inorganic particle filled organic polymer layers. Illustrative composite (e.g. passive) cooling films that comprises comprise reflective nonporous inorganic particle filled organic polymer layers are described in US11654664; incorporated by reference.

[0116] In some embodiments, such a layer may take the form of a premade inorganic particle filled film. By pre-made is meant that the layer already exists in a stable and handleable form prior to being combined with protective layers described herein. Such a premade inorganic particle filled film might be for a example a film of polymethylmethacrylate, or co-polymethylmethacrylate that is loaded with a suitable amount of reflective inorganic particles. In some embodiments, the reflective layer may be a painted layer derived from a suitable paint that comprises a suitable amount of reflective inorganic particles. Any such paint may be, for example, painted or otherwise coated onto a suitable substrate and then allowed to solidify. The painted substrate may be combined with other layers to form a passive radiative cooling film. Reflective organic polymer layer in further detail, reflective nonporous inorganic particle filled organic polymer layer may comprise a porosity of less than 10%.

[0117] Exemplary inorganic particles for inorganic particle filled organic polymer layer may be chosen from, for example, titanium dioxide, magnesium oxide, zinc oxide, calcium carbonate, hydroxy apatite, barium sulfate, silicon dioxide, zirconium dioxide, cerium oxide, aluminum silicate, kaolin-ite clay, and combinations and blends thereof. The inorganic particles may be present at any loading (weight percent, based on the total weight of the layer. By definition, an inorganic particle filled organic polymer layer will comprise at least 5 weight percent of reflective inorganic particles. In various embodiments, the reflective inorganic particles may comprise at least 10, 15, 20, 30, 40, 50, 60, or 70 weight percent of the inorganic particle filled organic polymer layer. The reflective inorganic particles may comprise any suitable average particle size and particle size distribution. In some embodiments at least 20, 40, 60, 80, or 90 percent (by number average) of the reflective inorganic particles may exhibit a diameter (or equivalent diameter if irregularly shaped) of less than 5.0, 2.0, or 1.0 microns. In some embodiments at least 90, 95, Or 98 percent of the inorganic particles may be nanoparticles with a diameter or equivalent diameter of less than 1000 nanometers. If desired, the particles may be surface treated to enhance the ability of the particles to be dispersed into the organic polymer material.

[0118] In some embodiments, the inorganic particle fdled organic polymer layer may take the form of a premade inorganic particle fdled organic polymer fdm, meaning that the reflective layer already exists in a stable and handleable form prior to being combined with other layers to form the cooling fdm.

[0119] Such premade inorganic particle fdled organic polymer fdm may be, for example, a fdm of polymethylmethacrylate (PMMA), or copolymethylmethacrylate (CoPMMA), or even a block copolymer CoPMMA such as those available from Kuraray, blended with barium sulfate, titanium dioxide, and / or calcium carbonate in sufficient amount. However, any suitable organic polymer material may be used as long as it exhibits sufficient mechanical properties and can be loaded with an acceptable amount of reflective inorganic particles. Any such layer may be combined with any other layers mentioned herein by, for example, being laminated together with such layers through the use of one or more layers of pressure sensitive adhesive.

[0120] In some embodiments the solidification of the organic polymer binder of a paint may not involve chemical reaction (formation of bonds). In other embodiments, the solidification may involve at least some bond formation, e.g., if the paint includes one or more thermosettable components, e.g., a drying oil such as linseed oil or the like. In general, an organic polymer binder of such a pamt may be chosen from, or include, materials such as alkyds, acrylics, vinyl acrylics, styrene-acrylics, vinyl acetate / ethylenes, polyurethanes, polyesters, melamine resins, epoxy resins, polysiloxanes, polylactic acid, cellulose, polysaccharides, and so on. In particular embodiments, such a binder may be an acrylic material comprising, e.g., polymethylmethacrylate and / or copolymers thereof. The binder will provide the solidified paint layer with, e.g., mechanical durability, toughness, abrasion resistance, and the like. The paint may include any other materials as are needed for any other purposes, e.g., leveling agents, viscosity modifiers, dyes, biocides, emulsifiers, and so on. Suitable paints that may be used to form a reflective layer useful for the purposes described herein may include those described, e.g., in U.S. Pat. No. 10,323,151, which is incorporated by reference herein forthis purpose. Examples of potentially suitable paints include products available from various sources, e g., Solarkote, SunTech Coatings, Tropi-Cool, SkyCool Pty Ltd, Sherwin Williams, and Exterior Performance Coatings. It will be appreciated that many such paints include one or more UV-blocking additives or the like.

[0121] The reflective layer may have an average reflectance of at least 85% (in some embodiments, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or even at least 99.5%) over a wavelength range of at least a 400 nm to 700 nm. Accordingly, in some embodiments, the reflective layer may have an average reflectance of at least 85% (in some embodiments, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or even at least 99.5%) over a wavelength range of at least a 300 nm to 2500 nm. Additives for Multilayer Optical Film and / or Protective Film

[0122] The multilayer film of the passive cooling article may further comprise UV-absorbers (UVAs) and Hindered Amine Light Stabilizers (HALs). Exemplary UVAs include those available under the trade designations “TINUVIN 1577” and “TINUVIN 1600,” from BASF Corporation, Florham Park, NJ. Typically, UVAs are incorporated in the polymer at a concentration of 1-10 wt%. Exemplary HALs include those available under the trade designations “CHIMMASORB 944” and “TINUVIN 123,” from BASF Corporation. Typically, the HALs are incorporated into the polymer at are 0.1-1.0 wt%. A 10: 1 ratio of UVA to HALs can be optimum.

[0123] The multilayer film of the passive cooling article may further comprise UV blocking additives such as small particle non-pigmentary zinc oxide and titanium oxide can also be used, especially in the skin layer. Nanoscale particles of zinc oxide and titanium oxide will reflect, or scatter, UV light while being transparent to visible and near infrared light. These small zinc oxide and titanium oxide particles that can reflect UV light are available, for example, in the size range of 10-100 nanometers from Kobo Products, Inc., South Plainfield, NJ.

[0124] The protective film may further comprise additives provided the additives to not detract from the high transmission of solar wavelengths of light.

[0125] In some embodiments, the protective film may further comprise anti-stat especially in the skin layer to reduce unwanted attraction of dust, dirt, and debris. Ionic salt anti-stats are available from 3M Company. Other anti-stat additives are available under the trade designation “STAT-RITE” from Lubrizol Engineered Polymers, Brecksville, OH, or under the trade designation “PELESTAT” from Sanyo Chemical Industries, Tokyo, Japan.

[0126] In some embodiments, the protective film may further low surface energy additives such as additives that contain fluorinated moieties, silane moieties, siloxane moieties, or combinations thereof.

[0127] Systems and Methods of Replacing / Replenishing the Protective Film

[0128] The protective film may optionally be attached to the first major surface of the solar article by any suitable means does that does not eliminate the air interface between the solar article and protective film. For example, the protective film may optionally be attached the the first major surface of the solar article with static energy, (e.g. low pressure) vacuum, a mechanical member or a combination thereof

[0129] In one embodiment, the protective film may be (temporarily) adhesively bonded or mechanically attached at the periphery edges to the solar article to prevent dirt, rain, and other contaminants from getting in between the protective film and solar article.

[0130] With reference to FIG. 4, in one embodiment, the solar article comprises frame members 420 attached by hinges 421. During use, the frame members 420 contact the protection film 450 at the periphery of the underlying solar article (not-shown). To replace the protection film, the frame members 420 can be disengaged by rotating each member (e.g. up to 180 degrees or more) about the axis of the hinges 421. The soiled piece of protection film can then be replaced with a clean piece. In other embodiments, the protective film is provided on the the first major surface of the solar article by use of a roll-to-roll system and method.

[0131] With reference to FIG. 5, in one embodiment, the roll-to-roll system 500 and method comprises a first (e g. unwind) roll 531 that comprises a roll of unsoiled (e.g. polyolefin) protection film and a second (e.g. winding) roll 532 that comprises soiled (e.g. polyolefin) protection film. Unsoiled protection film of roll 531 is conveyed across the surface 511 of solar article 510 by the winding action of roll 532. The winding action of the second roll 532 can be continuous or intermittent. In one embodiment, the winding action is in response to data regarding the performance (e.g. electrial output) of the solar article or a sensor monitoring the transparency of the protection film. When the electrical output or transparency drops below a determined threshold value, the second (e.g. winding) roll 532 turns on for a predetermined period of time based on the dimensions of the solar article thereby conveying unsoiled protection film across the surface of the solar article and winding the soiled film onto second roll 532. When second roll 532 encounter resistance due to roll 531 reaching the end of the roll, roll 532 of soiled protective film is removed and disgarded or recycled. A new roll of unsoiled protection film is placed on the first roll 531. The leading edge of the protection film is attached to the second (e.g. winding) roll 532 with the protection film between the rolls being proximate to the first major surface of the underlying solar article.

[0132] With reference to FIG. 6, in another embodiment, the roll-to-roll system 600 and method comprises a first (e.g. unwind) roll 631 and a second (e.g. winding) roll 632. A continuous loop of protection film 650 is conveyed around solar article 610. Unsoiled protection film is conveyed from roll 631 across the first major surface 611 of solar article 610 by the winding action of roll 632. The winding action of the second roll 632 can be continuous or intermittent. After reaching roll 632, the soiled protection film is conveyed below the opposing second major surface 612 of solar artilce 610.

[0133] In this emboidment, the soiled protection film is typically conveyed through a cleaning apparatus 480. Various cleaning apparatus can be used including (e.g. spraying) water, brushes, etc. In one embodiment, the cleaning apparatus 680 includes a first roller 681 that includes a (e.g. low tack) pressure sensitive adhesive for cleaning the first major surface 651 of the protection film 650. The cleaning apparatus 680 optionally includes a second roller 682 that includes a (e.g. low tack) pressure sensitive adhesive for cleaning the second major surface 652 of the protection film 650. Roller 681 and optionally 682 can be part of a roll-to-roll system wherein a pressure sensitive adhesive coated film is utilized to clean the protection film and then replaced with a new piece of pressure sensitive adhesive coated film in the same manner as described for replacing the protection film of FIG. 5. Alternatively, roller 681 and optionally roller 682 may comprise a roll of pressure sensitive adhesive coated films having scoring amenable to removing a sheet of pressure sensitive adhesive coated film from the roll (similar to that of a lint roller). The same piece of pressure sensitive adhesive coated film may repeatedly be used to clean the protection film until the pressure sensitive adhesive coated film no longer effectively cleans the protection film. The pressure sensitive adhesive coated film may further comprise a tab to faciliate removal of a single piece of pressure sensitive adhesive coated film by a person or robot. The cleaning effectiveness can be monitored in response to data regarding the performance (e g. electrial output) of the solar article or a sensor monitoring the transparency of the protection film, as previously described

[0134] Although the roll-to-roll systems 500 and 600 and methods are depicted in a horizontal arrangement, in typical applications the solar article and protection film system would be angled relative to the sun. For example, the solar panel may be positioned at an angle ranging from 5 degrees to 90 degress relative to a Cartesina coordinate system having a horizontal x-axis and vertical y-axis. When the solar article and protection film system are angled, the system can also be amendable to snow removal. Further, the first (e.g. unwind) roll 431 and second (e.g. winding) roll 432 may be equipped with a mechanism that allows positioning of the rolls. For example, it may be advantageous to elevate the rolls above the solar article while the protection film is being conveyed to avoid dragging the protective film across the surface of the solar article. Further, is may be advantageous to position the rolls (531, 532, 631, 632) slightly below the first major surface (511, 611) of the solar article in order pull the protection film in close contact with the first major surface of the solar article (510, 610).

[0135] Examples

[0136] Test Method

[0137] Transmission can be measured with methods described in ASTM E1348-15el (2015). A Lambda 1050 spectrophotometer equipped with an integrating sphere was used to make transmission measurements described herein. The Lambda 1050 was configured to scan from 250 nanometer wavelengths of light to 2500 nanometer wavelengths of light at 5 nanometer intervals in transmission mode. Background scans are conducted with no sample in the light path before the integrating sphere, and the standard spectralon covers over the integrating sphere ports. After background scans are made, the film sample is placed in the light path by covering the entrance port to the integrating sphere with the film sample. Light transmission spectrum scans are made using the standard detectors for a range from 250 nanometers to 2500 nanometers and recorded by the software provided with the Lambda 1050.

[0138] FTIRtest method for3300 to 25000 nm. Transmission data from 3300nm to 25000nm was measured with an FTIR spectrophotometer model Nicolett iS50 available from Thermo Fisher following methods described in ASTM El 421.

[0139] A polyolefin film comprising a structured surface was prepared having a structured surface according to FIG. 3. LDPE 9551 available from Dow Corporation was extrusion replicated on an extrusion replication casting roll created by a diamond turning machine (DTM) method. LDPE 9551 is reported to have a density of 0.923 g / cc and a melt index of 35 g / 10 min. The casting roll had the negative replication of the structured surface depicted in FIG. 3. The LDPE 9551 was extruded at an extrusion rate of 40.8kg / hr onto the extrusion replication casting roll having a surface temperature of 82.2C and speed of 12.2 meters per minute. A nip force of 4136.9 kPa was applied to the LDPE polymer melt curtain with a matte rubber nip roll as it contacted the extrusion replication casting roll tool. The dimensions with respect to the reference numerals of FIG. 3 are as follows:

[0140] Nanostructured Micro-space

[0141] 340 = 250 nm

[0142] 346 = 178.6 nm

[0143] B = 70 degrees

[0144] Nanostructured Micro-peak

[0145] 340 = 250 nm

[0146] 346 = 118.5 nm

[0147] B= 70 degrees

[0148] Micro-peak

[0149] 242 = 150 microns

[0150] 244 = 80 microns

[0151] 246 = 80 microns

[0152] A = 53.13 degrees

[0153] Transmission Results

[0154] The transmission of the structured LDPE fdm was compared to unstructured LDPE file using the test method described above.

[0155] The transmission results were as follows:

[0156] Both the structured and unstructured film had a transmission of at least 94, 95, 96, 97, 98 or 99% for wavelengths in the range of 0.25 microns to 0.26 microns and the structured LDPE film had a % transmission 1-2% greater than the unstructured film for this wavelength range.

[0157] Both the structured and unstructured film had a transmission of at least 95, 96, 97, or 98% for wavelengths in the range of 0.26 microns to 2.40 microns and the structured LDPE film had a % transmission 3% to 4.5% greater than the unstructured film for this wavelength range.

[0158] Both the structured and unstructured film had a transmission of at least 95, 96, 97, or 98% for wavelengths in the range 2.40 microns to 3.31 microns and the structured LDPE film had a % transmission 1-2% greater than the unstructured film.

[0159] For wavelength in the range of 3.31 microns to 3.44 microns the unstructured LDPE film had a transmission of at least 95, 96, or 97%. The structured LDPE film had a lower % transmission than the unstructured film. The lowest value was 9% for a wavelength of 3.36. The unstructured LDPE had a transmission of about 96% for a wavelength of 3.36.

[0160] For the wavelengths in the range of 3.44 microns to 3.54 microns, both the structured and unstructured LDPE films had a transmission of at least 95, 96, 97, or 98% and the % transmission of the films differed by less than 1%. Both the structured and unstructured film had a transmission of at least 95, 96, 97, or 98% for wavelengths in the range of 3.54 microns to 25.00 microns. The structured LDPE film had a % transmission 1-2% greater than the unstructured film for this wavelength range.

[0161] Overall the structured film has a greater transmission since the intensity of solar radiation at the wavelength band of 3.31 microns to 3.44 microns is small in companson to the remainder of the wavelength band.

[0162] Due to the greater transmission, the structured protective film would improve the efficiency of solar articles as compared to unstructured protective film.

Claims

What is claimed is:

1. A system comprising: a solar article having a first major surface that faces the sun during daytime use and an opposing second major surface; a protective film having first major surface that faces the sun during daytime use and an opposing second major surface; wherein the first major surface ofthe solar article and / or the opposing second major surface of the protective film comprises structures having at least two dimensions less than 1 mm that provide an air interface between the first major surface of the solar article and the second major surface of the protective film.

2. The system of claim 1 wherein the second major surface of the protective film is not chemically, thermally, or adhesively bonded to the first major surface of the solar article.

3. The system of claims 1-2 wherein the protective film is attached to the solar article with static energy, vacuum, a mechanical member, or a combination thereof.

4. The system of claims 1-3 wherein the first major surface of the solar article comprises the structures.

5. The system of claims 1-4 wherein the second major surface of the protective film comprises the structures.

6. The system of claims 1-5 wherein the first major surface of the protective film further comprises structures.

7. The system of claims 1-6 wherein the structures comprise microstructures, nanostructures, or a combination thereof.

8. The system of claims 1-7 wherein the structures comprise peak structures having an apex angle ranging from 20 degrees to 120 degrees.

9. The system of claim 1-8 wherein the structures comprise nanostructures.

10. The system of claims 1-9 wherein the protective film has one or more of the following properties: i) a transmission of at least 95, 96, 97, 98, or 99% for wavelengths ranging from greater than 0.75 microns (750 nm) to 3.3 microns (3300 nm); ii) a transmission of at least 95, 96, 97, 98, or 99% at wavelengths ranging from greater than 3.6 microns (3600 nm) to 25.0 microns (25000 nm);iii) wherein the protective film comprises the structures and the protective film has a transmission at leastI, 2, 3, 4, or 5% greater than the same protective film lacking structures for wavelengths ranging from 0.75 microns to 3.3 microns or for wavelengths ranging from 3.6 microns to 25.0 microns.I I. The system of claims 1-10 wherein the solar article is a photovoltaic module.

12. The system of claims 1-11 wherein the protective film comprises a polyolefin material.

13. The system of claims 1-12 wherein the solar article is a passive radiative cooling heat transfer panel.

14. The system of claims 1-12 wherein the solar article is a cooling film.

15. The system of claim 1-14 wherein the solar article comprises a multilayer film.

16. The system of claims 14-15 wherein cooling film is a microporous composite cooling film or a non- porous cooling film comprising an organic polymer film and inorganic reflective particles.

17. The system of claims 1-16 wherein the multilayer film lacks a fluorinated material.

18. The system of claims 1-17 wherein the protective film is conveyed across the first major surface of the solar article with a roll to roll apparatus.

19. The system of claims 1-18 wherein the system further comprises an apparatus for cleaning at least the first major surface of the protective film and optionally the opposing major surface.

20. The system of claim 19 wherein the apparatus for cleaning comprises a pressure sensitive adhesive on a roll.

21. The system of claims 19-20 further comprising conveying the cleaned protective film across the major surface of the solar article.

22. A structured polyolefin film suitable for use as a protective film for a solar article according to claims 6-10.

23. A method of improving the efficiency of a solar article comprising providing a solar article having a first major surface that faces the sun during daytime use and an opposing second major surface;providing a protective film having first major surface that faces the sun during daytime use and an opposing second major surface; wherein the the protective film proximate the first major surface of the solar article; and wherein the first major surface of the solar article and / or the opposing second major surface of the protective film comprises structures having at least two dimensions less than 1 mm that provide an air interface between the first major surface of the solar article and the second major surface of the protective film.

24. The method of claim 23 wherein the method is further characterized by claims 2-22.

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