Durable solar mirror films

Abstract

The present disclosure generally relates to durable solar mirror films, methods of making durable solar mirror films, and constructions including durable solar mirror films. In one embodiment, the present disclosure relates to a solar mirror film comprising: a multilayer optical film layer including having a coefficient of hygroscopic expansion of less than about 30 ppm per percent relative humidity; and a reflective layer having a coefficient of hygroscopic expansion.

Claims

1. A solar mirror film comprising: a multilayer optical film layer including having a coefficient of hygroscopic expansion of less than about 30 ppm per percent relative humidity; a reflective layer, and a tie layer between the multilayer optical film layer and the reflective layer, wherein the reflective layer is a metal layer, and wherein the tie layer comprises titanium dioxide.

2. The solar mirror film of claim 1, wherein the coefficient of hygroscopic expansion of the multilayer optical film layer is between about 25 ppm per percent relative humidity and about 5 ppm per percent relative humidity.

3. The solar mirror film of claim 1, wherein the reflective layer comprises at least one of silver, gold, aluminum, copper, nickel, and titanium.

4. The solar mirror film of claim 1, wherein the reflective layer has a coefficient of hygroscopic expansion that is between 0 ppm per percent relative humidity and 3 ppm per percent relative humidity.

5. The solar mirror film of claim 1, further comprising: a weatherable layer adjacent to the multilayer optical film layer.

6. The solar mirror film of claim 1, wherein the multilayer optical film layer exhibits an average radiation reflectivity of at least 90% over a portion of the solar radiation wavelength range from 380 nm to 3,000 nm.

7. The solar mirror film of claim 1, wherein the coefficient of hygroscopic expansion of the multilayer optical film layer is between about 10 ppm per percent relative humidity and about 25 ppm per percent relative humidity.

8. The solar mirror film of claim 1, wherein the coefficient of hygroscopic expansion of the multilayer optical film layer is between about 15 ppm per percent relative humidity and about 20 ppm per percent relative humidity.

9. The solar mirror film of claim 1, further comprising: a compliance layer between the multilayer optical film layer and the reflective layer.

10. The solar mirror film of claim 9, wherein the compliance layer comprises butyl acrylate.

11. The solar mirror film of claim 1, further comprising: a corrosion protective layer adjacent to the reflective layer.

12. The solar mirror film of claim 11, wherein the corrosion protective layer comprises at least one of copper and an inert metal alloy.

13. The solar mirror film of claim 1, further including an adhesive layer adjacent to the reflective layer.

14. The solar mirror film of claim 13, wherein the adhesive layer is between the reflective layer and a substrate.

15. The solar mirror film of claim 1, further comprising: a substrate.

16. The solar mirror film of claim 1, wherein the solar mirror film is incorporated into a reflector assembly.

17. The solar mirror film of claim 1, wherein the solar mirror film includes one or more skin layers including PMMA and PVDF.

18. The solar mirror film of claim 1 claim 1, wherein the solar mirror film includes one or more optical layers including a blend of PMMA and PVDF.

19. A concentrated photovoltaic system, comprising the solar mirror film of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view of a prior art solar mirror film.

(2) FIG. 2 is a schematic view of one exemplary embodiment of a solar mirror film in accordance with the present disclosure.

(3) FIG. 3 is a schematic view of another exemplary embodiment of a solar mirror film in accordance with the present disclosure.

(4) FIG. 4 is a schematic view of another exemplary embodiment of a solar mirror film in accordance with the present disclosure.

(5) FIG. 5 is a schematic view of another exemplary embodiment of a solar mirror film in accordance with the present disclosure.

DETAILED DESCRIPTION

(6) Some embodiments of the present application relate to the inclusion of a multilayer optical film as the weatherable layer of a solar mirror film. The multilayer optical film (MOF) has a CHE that is between the CHE of typically used weatherable layers (e.g., acrylics) and the CHE of the reflective layer. As such, the multilayer optical film lowers the stress differential caused by the disparity in CHEs of the weatherable layer and the reflective layer.

(7) One exemplary embodiment is shown schematically in FIG. 2. Solar mirror film 200 of FIG. 2 includes a premask layer 110, a MOF weatherable layer 220, a thin, sputter-coated tie layer 140, a reflective layer 150 (including, for example, a reflective metal such as silver), a corrosion resistant layer 160 (including, for example, a metal such as copper), an adhesive layer 170, and a liner 180.

(8) Another exemplary embodiment is shown schematically in FIG. 3. Solar mirror film 300 includes a premask layer 110, a MOF weatherable layer 220, a compliance layer 310 (including, for example, an butyl acrylate), a thin, sputter-coated tie layer 140, a reflective layer 150 (including, for example, a reflective metal such as silver), a corrosion resistant layer 160 (including, for example, a metal such as copper), an adhesive layer 170, and a liner 180.

(9) Another exemplary embodiment is shown schematically in FIG. 4. Solar mirror film 400 includes a premask layer 110, a PMMA layer 410, an adhesive layer 420, a MOF weatherable layer 220, a thin, sputter-coated tie layer 140, a reflective layer 150 (including, for example, a reflective metal such as silver), a corrosion resistant layer 160 (including, for example, a metal such as copper), an adhesive layer 170, and a liner 180. Some implementations of this embodiment also include a compliance layer, as shown schematically in FIG. 3 and described below.

(10) Another exemplary embodiment is shown schematically in FIG. 5. Solar mirror film 500 includes a premask layer 110, a compliance layer 310, a MOF weatherable layer 220, a thin, sputter-coated tie layer 140, a reflective layer 150 (including, for example, a reflective metal such as silver), a corrosion resistant layer 160 (including, for example, a metal such as copper), an adhesive layer 170, and a liner 180.

(11) For purposes of clarity, all layers in the various embodiments shown in FIGS. 1-5 and described herein are optional except for the MOF layer and the reflective layer. Each layer that could be included in a solar mirror film of the types generally described herein is discussed in detail below.

(12) Premask Layer

(13) The premask layer is optional. Where present, the premask protects the weatherable layer during handling, lamination, and installation. Such a configuration can then be conveniently packaged for transport, storage, and consumer use. In some embodiments, the premask is opaque to protect operators during outdoor installations. In some embodiments, the premask is transparent to allow for inspection for defects. Any known premask can be used. One exemplary commercially available premask is ForceField 1035 sold by Tredegar of Richmond, Va.

(14) Multilayer Optical Film Layer

(15) Exemplary multilayer optical films of the present disclosure may be prepared, for example, using the apparatus and methods disclosed in U.S. Pat. No. 6,783,349, entitled Apparatus for Making Multilayer Optical Films, U.S. Pat. No. 6,827,886, entitled Method for Making Multilayer Optical Films, and PCT Publication Nos. WO 2009/140493 entitled Solar Concentrating Mirror and WO 2011/062836 entitled Multi-layer Optical Films, all of which are incorporated herein by reference in their entireties. In WO 2009/140493, PMMA/PVDF skin layers are described. Examples of additional layers or coatings suitable for use with exemplary multilayer optical films of the present disclosure are described, for example, in U.S. Pat. Nos. 6,368,699, and 6,459,514 both entitled Multilayer Polymer Film with Additional Coatings or Layers, both of which are incorporated herein by reference in their entireties.

(16) In some embodiments, the weatherable MOF layer may have spectral regions of high reflectivity (>90%) and other spectral regions of high transmissivity (>90%). In some embodiments, the weatherable layer provides high optical transmissivity over a portion of the solar spectrum and low haze and yellowing, good weatherability, good abrasion, scratch, and crack resistance during to handling and cleaning, and good adhesion to other layers, for example, other (co)polymer layers, metal oxide layers, and metal layers applied to one or both major surfaces of the films when used as substrates, for example, in compact electronic display and/or solar energy applications.

(17) Inclusion of the multilayer optical film in the solar mirror film construction can, in some embodiments, be introduced as in-line processes.

(18) Inclusion of the multilayer optical film in the solar mirror film confers various advantages. The multilayer optical film has a coefficient of hygroscopic expansion that is between the coefficient of hygroscopic expansion of prior art weatherable layers and the reflective layer. In some embodiments, the multilayer optical film has a coefficient of hygroscopic expansion that is less than 30 ppm per percent RH. In some embodiments, the multilayer optical film has a coefficient of hygroscopic expansion of between about 10 ppm per percent relative humidity and about 25 ppm per percent relative humidity. In some embodiments, the multilayer optical film has a coefficient of hygroscopic expansion of between about 15 ppm per percent relative humidity and about 20 ppm per percent relative humidity.

(19) Prior art weatherable films have a coefficient of hygroscopic expansion of at least about 30 ppm per percent RH. In some embodiments, the coefficient of hygroscopic expansion of the multilayer optical film is between about 75% and about 25% of the coefficient of hygroscopic expansion of the prior art weatherable layers. In some embodiments, the coefficient of hygroscopic expansion of the multilayer optical film is between about 70% and about 30% of the coefficient of hygroscopic expansion of the prior art weatherable layers. In some embodiments, the coefficient of hygroscopic expansion of the multilayer optical film is between about 60% and about 40% of the coefficient of hygroscopic expansion of the prior art weatherable layers.

(20) Tie Layer

(21) In some embodiments, the tie layer includes a metal oxide such as aluminum oxide, copper oxide, titanium dioxide, silicon dioxide, or combinations thereof. As a tie layer, titanium dioxide was found to provide surprisingly high resistance to delamination in dry peel and wet peel testing. Further options and advantages of metal oxide tie layers are described in U.S. Pat. No. 5,361,172 (Schissel et al.), incorporated by reference herein.

(22) In any of the foregoing exemplary embodiments, the tie layer has a thickness of equal to or less than 500 micrometers. In some embodiments, the tie layer has a thickness of between about 0.1 micrometer and about 5 micrometers. In some embodiments, it is preferable that the tic layer have an overall thickness of at least 0.1 nanometers, at least 0.25 nanometers, at least 0.5 nanometers, or at least 1 nanometer. In some embodiments, it is preferable that the tie layer have an overall thickness no greater than 2 nanometers, no greater than 5 nanometers, no greater than 7 nanometers, or no greater than 10 nanometers.

(23) Compliance Layer

(24) In some embodiments, the solar mirror film includes a compliance layer. Compliance layers are preferably non-tacky at ambient temperatures. In some embodiments, the compliance layer includes poly(methyl methacrylate) and a first block copolymer having at least two endblock polymeric units that are each derived from a first monoethylenically unsaturated monomer comprising a methacrylate, acrylate, styrene, or combination thereof, wherein each endblock has a glass transition temperature of at least 50 degrees Celsius; and at least one midblock polymeric unit that is derived from a second monoethylenically unsaturated monomer comprising a methacrylate, acrylate, vinyl ester, or combination thereof, wherein each midblock has a glass transition temperature no greater than 20 degrees Celsius.

(25) Alternatively, in some embodiments, the compliance layer includes a block copolymer/homopolymer blend. For example, the compliance layer may include an A-B-A triblock copolymer blended with a homopolymer that is soluble in either the A or B block. Optionally, the homopolymer has a polymeric unit identical to either the A or B block. The addition of one or more homopolymers to the block copolymer composition can be advantageously used either to plasticize or to harden one or both blocks. In preferred embodiments, the block copolymer contains a poly(methyl methacrylate) A block and a poly(butyl acrylate) B block, and is blended with a poly(methyl methacrylate) homopolymer.

(26) Advantageously, blending poly(methyl methacrylate) homopolymer with poly(methyl methacrylate)-poly(butyl acrylate) block copolymers allows the hardness to be tailored to the desired application. As a further advantage, blending with poly(methyl methacrylate) provides this control over hardness without significantly degrading the clarity or processibility of the overall composition. Preferably, the homopolymer/block copolymer blend has an overall poly(methyl methacrylate) composition of at least 30 percent, at least 40 percent, or at least 50 percent, based on the overall weight of the blend. Preferably, the homopolymer/block copolymer blend has an overall poly(methyl methacrylate) composition no greater than 95 percent, no greater than 90 percent, or no greater than 80 percent, based on the overall weight of the blend.

(27) Particularly suitable non-tacky block copolymers include poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) (25:50:25) triblock copolymers. These materials were previously available under the trade designation LA POLYMER from Kuraray Co., LTD.

(28) Optionally, the block copolymer may be combined with a suitable ultraviolet light absorber to enhance the stability. In some embodiments, the block copolymer contains an ultraviolet light absorber. In some embodiments, the block copolymer contains an amount of the ultraviolet light absorber ranging from 0.5 percent to 3.0 percent by weight, based on the total weight of the block copolymer and absorber. It is to be noted, however, that the block copolymer need not contain any ultraviolet light absorbers. Using a composition free of any ultraviolet light absorbers can be advantageous because these absorbers can segregate to the surfaces and interfere with adhesion to adjacent layers.

(29) In some embodiments, the block copolymer may be combined with one or more nanofillers to adjust the modulus of the compliance layer. For example, a nanofiller such as silicon dioxide or zirconium dioxide can be uniformly dispersed in the block copolymer to increase the overall stiffness or hardness of the solar mirror film. In preferred embodiments, the nanofiller is surface-modified as to be compatible with the polymer matrix.

(30) In some embodiments, the compliance layer includes a random copolymer having a first polymeric unit with a relatively high T.sub.g and second polymeric unit with a relatively low T.sub.g. In this embodiment, the first polymeric unit derives from a first monoethylenically unsaturated monomer comprising a methacrylate, acrylate, styrene, or combination thereof and associated with a glass transition temperature of at least 50 degrees Celsius and the second polymeric unit derived from a second monoethylenically unsaturated monomer comprising a methacrylate, acrylate, vinyl ester, or combination thereof and associated with a glass transition temperature no greater than 20 degrees Celsius. In some preferred random copolymers, the first polymeric unit is methyl methacrylate and the second polymeric unit is butyl acrylate. It is preferable that the random copolymer has a methyl methacrylate composition of at least 50 percent, at least 60 percent, at least 70 percent, or at least 80 percent, based on the overall weight of the random copolymer. It is further preferable that the random copolymer has a methyl methacrylate composition of at most 80 percent, at most 85 percent, at most 90 percent, or at most 95 percent, based on the overall weight of the random copolymer.

(31) In some embodiments, the compliance layer has a thickness of at least 10 micrometers, at least 50 micrometers, or at least 60 micrometers. Additionally, in some embodiments, the compliance layer has a thickness no greater than 200 micrometers, no greater than 150 micrometers or no greater than 100 micrometers. In some embodiments, the compliance layer has a thickness no greater than 5 micrometers. In some such embodiments, the compliance layer has a thickness of from 0.1 micrometer to 3 micrometers.

(32) Reflective Layer

(33) The solar mirror films described herein include one or more reflective layers. Besides providing a high degree of reflectivity, the reflective layer(s) can provide manufacturing flexibility. Optionally, the reflective layer may be applied onto a relatively thin organic tic layer or inorganic tic layer, which is in turn situated on a weatherable layer.

(34) In some embodiments, the reflective layer(s) have smooth, reflective metal surfaces that are specular. As used herein, the term specular surfaces refer to surfaces that induce a mirror-like reflection of light in which the direction of incoming light and the direction of outgoing light form the same angle with respect to the surface normal. Any reflective metal may be used for this purpose, although preferred metals include silver, gold, aluminum, copper, nickel, and titanium. In some embodiments, the reflective layer includes elemental silver.

(35) The reflective layer has a coefficient of hygroscopic expansion of about zero ppm per percent RH. In some embodiments, the reflective layer has a coefficient of hygroscopic expansion of between about zero ppm per percent RH and about 3 ppm per percent RH.

(36) The reflective layer need not extend across the entire major surface of the weatherable layer. If desired, the weatherable layer can be masked during the deposition process such that the reflective layer is applied onto only a pre-determined portion of the weatherable layer.

(37) Patterned deposition of the reflective layer onto the multilayer optical film or weatherable layer is also possible. Exemplary ways of creating a pattern in the reflective layer are described, for example, in matter numbers 69678US002, 69677US002, and 69681US002, all assigned to the present applicant and all incorporated herein in their entirety.

(38) Application of the metal to the polymer can be achieved using numerous coating methods including, for example, physical vapor deposition via sputter coating, evaporation via e-beam or thermal methods, ion-assisted e-beam evaporation, electro-plating, spray painting, vacuum deposition, and combinations thereof. The metallization process is chosen based on the polymer and metal used, the cost, and many other technical and practical factors.

(39) Physical vapor deposition (PVD) of metals is very popular for some applications because it provides the purest metal on a clean interface. In this technique, atoms of the target are ejected by high-energy particle bombardment so that they can impinge onto a substrate to form a thin film. The high-energy particles used in sputter-deposition are generated by a glow discharge, or a self-sustaining plasma created by applying, for example, an electromagnetic field to argon gas.

(40) In one exemplary method, the deposition process continues for a sufficient duration to build up a suitable layer thickness of the reflective layer on the weatherable layer, thereby forming the reflective layer.

(41) The reflective layer is preferably thick enough to reflect the desired amount of the solar spectrum of light. The preferred thickness can vary depending on the composition of the reflective layer. In some exemplary embodiments, the reflective layer is between about 75 nanometers to about 100 nanometers thick for metals such as silver, aluminum, copper, and gold. Although not shown in the figures, two or more reflective layers may be used.

(42) In some embodiments, the reflective layer has a thickness no greater than 500 nanometers. In some embodiments, the reflective layer has a thickness of from 80 nm to 250 nm. In some embodiments, the reflective layer has a thickness of at least 25 nanometers, at least 50 nanometers, at least 75 nanometers, at least 90 nanometers, or at least 100 nanometers. Additionally, in some embodiments, the reflective layer has a thickness no greater than 100 nanometers, no greater than 110 nanometers, no greater than 125 nanometers, no greater than 150 nanometers, no greater than 200 nanometers, no greater than 300 nanometers, no greater than 400 nanometers, or no greater than 500 nanometers.

(43) Corrosion Resistant Layer

(44) The corrosion resistant layer is optional. Where included, the corrosion resistant layer may include, for example, elemental copper. Use of a copper layer that acts as a sacrificial anode can provide a reflective article with enhanced corrosion-resistance and outdoor weatherability. As another approach, a relatively inert metal alloy such as Inconel (an iron-nickel alloy) can also be used.

(45) The corrosion resistant layer is preferably thick enough to provide the desired amount of corrosion resistance. The preferred thickness can vary depending on the composition of the corrosion resistant layer. In some exemplary embodiments, the corrosion resistant layer is between about 75 nanometers to about 100 nanometers thick. In other embodiments, the corrosion resistant layer is between about 20 nanometers and about 30 nanometers thick. Although not shown in the figures, two or more corrosion resistant layers may be used.

(46) In some embodiments, the corrosion resistant layer has a thickness no greater than 500 nanometers. In some embodiments, the corrosion resistant layer has a thickness of from 80 nm to 250 nm. In some embodiments, the corrosion resistant layer has a thickness of at least 25 nanometers, at least 50 nanometers, at least 75 nanometers, at least 90 nanometers, or at least 100 nanometers. Additionally, in some embodiments, the corrosion resistant layer has a thickness no greater than 100 nanometers, no greater than 110 nanometers, no greater than 125 nanometers, no greater than 150 nanometers, no greater than 200 nanometers, no greater than 300 nanometers, no greater than 400 nanometers, or no greater than 500 nanometers.

(47) Adhesive Layer

(48) The adhesive layer is optional. Where present, the adhesive layer adheres the multilayer construction to a substrate (not shown in the figures). In some embodiments, the adhesive is a pressure sensitive adhesive. As used herein, the term pressure sensitive adhesive refers to an adhesive that exhibits aggressive and persistent tack, adhesion to a substrate with no more than finger pressure, and sufficient cohesive strength to be removable from the substrate. Exemplary pressure sensitive adhesives include those described in PCT Publication No. WO 2009/146227 (Joseph, et al.), incorporated herein by reference.

(49) Liner

(50) The liner is optional. Where present, the liner protects the adhesive and allows the solar mirror film to be transferred onto and another substrate. Such a configuration can then be conveniently packaged for transport, storage, and consumer use. In some embodiments, the liner is a release liner. In some embodiments, the liner is a silicone-coated release liner.

(51) Substrate

(52) The films described herein can be applied to a substrate by removing liner 180 (where present) and placing adhesive layer 170 (where present) adjacent to the substrate. Premask layer 110 (where present) is then removed to expose weatherable layer 120 to sunlight. Suitable substrates generally share certain characteristics. Most importantly, the substrate should be sufficiently rigid. Second, the substrate should be sufficiently smooth that texture in the substrate is not transmitted through the adhesive/metal/polymer stack. This, in turn, is advantageous because it: (1) allows for an optically accurate mirror, (2) maintains physical integrity of the metal reflective layer by eliminating channels for ingress of reactive species that might corrode the metal reflective layer or degrade the adhesive, and (3) provides controlled and defined stress concentrations within the reflective film-substrate stack. Third, the substrate is preferably nonreactive with the reflective mirror stack to prevent corrosion. Fourth, the substrate preferably has a surface to which the adhesive durably adheres.

(53) Exemplary substrates for reflective films, along with associated options and advantages, are described in PCT Publication Nos. WO04114419 (Schripsema), and WO03022578 (Johnston et al.); U.S. Publication Nos. 2010/0186336 (Valente, et al.) and 2009/0101195 (Reynolds, et al.); and U.S. Pat. No. 7,343,913 (Neidermeyer). For example, the article can be comprised in one of the many mirror panel assemblies as described in co-pending and co-owned provisional U.S. patent application Ser. No. 13/393,879 (Cosgrove, et al.). Other exemplary substrates include metals, such as, for example, aluminum, steel, glass, or composite materials.

(54) Those of skill in the art will appreciate that the embodiments described herein can include additional materials or layers. For example, some embodiments may include a compliant layer as is described in U.S. Patent Application Matter No. 69682US002, assigned to the present assignee and incorporated herein by reference in its entirety. Some embodiments may have less or no silver on the edge regions of the solar mirror film, as is described in U.S. Patent Application Matter No. 69678US002, assigned to the assignee of the present disclosure and incorporated herein by reference in its entirety.

(55) Advantages and embodiments of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. These examples are merely for illustrative purposes and are not meant to be limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Also, in these examples, all percentages, proportions and ratios are by weight unless otherwise indicated.

EXAMPLES

(56) Test Methods:

(57) Coefficient of Hygroscopic Expansion (CHE):

(58) Hygroscopic expansion was measured using a dynamic mechanical analyzer (DMA) (model Q800 obtained from TA Instruments) coupled with a DMA-RH accessory (obtained from TA Instruments). Displacement (in m/m) was measured over a ramp of varying relative humidities, ranging from about 20% to about 80% at a constant temperature of 25 C. Changes in the sample dimensions caused by humidity changes are used to calculate the CHE. Results are expressed in parts per million (ppm) per percent relative humidity (% RH).

(59) Neutral Salt Spray Test (NSS)

(60) Corrosion of the comparative and examples was evaluated following the procedure outlined on ISO 9227:2006, Corrosion tests in artificial atmospheresSalt spray tests with the exception that results are reported as visual observations after various times.

Comparative Example

(61) A silver metallized acrylic film (ECP-305+ manufactured by 3M Company, St. Paul, Minn.) was provided. This film looked substantially the same as the film shown in FIG. 1 except that it did not include tie layer 140. The silver metallized acrylic film had a CHE of 30 ppm per percent RH. The ECP-305+ film was laminated to a painted aluminum substrate using the PSA included in the product. The sample was cut to 44 using a shear cutter. The sample was weather tested according to the NSS described above and was found to exhibit tunneling in less than 72 hours.

Example 1

(62) A multilayer optical film was prepared as following: a multilayer optical stack (described below) was prepared by coextruding first and second polymer layers through a multilayer polymer melt manifold to create a multilayer melt stream having five-hundred and fifty alternating layers. Two skin layers each having a thickness of approximately 4 microns were also co-extruded as protective layers on each side of the optical layer stack. The multilayer melt stream was cast onto a chilled roll creating a multilayer cast web. The multilayer cast web was then heated in a tenter oven to a temperature of about 105 C. prior to being biaxially oriented to a draw ratio of 3.8 by 3.8. A silver reflective layer approximately 100 nm thick was vapor deposited onto the film substrate. A copper layer approximately 80 nm thick was coated onto the silver layer. A 25 micron acrylic adhesive was coated onto the copper layer. The resulting multilayer optical film was bonded to an epoxy coated aluminum substrate having a thickness of about 0.5 mm. The laminated sample was cut to 44 using a shear cutter.

(63) The first polymer layer of the multilayer stack was a birefringent layer including polyethylene terephtalate (PET) (obtained under the trade designation PET 9921, sold by Eastman Chemical Company), and an ultraviolet absorber (obtained under the trade designation SUKANO UV MASTERBATCH TA07-07, sold by Sukano Polymers Corporation, Duncan, S.C.) compounded at about 10 weight percent (wt %). The second polymer layer included a copolymer of polymethyl(meth)acrylate (co-PMMA) (obtained under the trade designation ATOGLAS 510A, sold by Arkema, King of Prussia, Pa.). The skin layers included a polymer blend comprising 35% polyvinylidene fluoride (PVDF) (obtained under the trade designation DYNEON PVDF 6008, sold by 3M Company) and 65% polymethyl(meth)acrylate (PMMA) (obtained under the trade designation CP-82, sold by Plaskolite, Columbus, Ohio), and which included 2.5 wt % of a second ultraviolet absorber

(64) The hygroscopic expansion of the multilayer MOF film was measured as described above and determined to be about 15 ppm per percent RH.

(65) The laminated film sample was weather tested as described above and was found not to exhibit tunneling after 1500 hours.

Example 2

(66) A multilayer optical film was prepared as following: a multilayer optical stack (described below) was prepared by coextruding first and second polymer layers through a multilayer polymer melt manifold to create a multilayer melt stream having one hundred and fifty alternating layers. Two skin layers each having a thickness of approximately 4 microns were also co-extruded as protective layers on each side of the optical layer stack. The multilayer melt stream was cast onto a chilled roll creating a multilayer cast web. The multilayer cast web was then heated in a tenter oven to a temperature of about 105 C. prior to being biaxially oriented to a draw ratio of 3.8 by 3.8. A silver reflective layer approximately 100 nm thick can be vapor deposited onto the film substrate. A copper layer approximately 80 nm thick can be coated onto the silver layer. A 25 micron acrylic adhesive can be coated onto the copper layer. The resulting multilayer optical film can be bonded to an epoxy coated aluminum substrate having a thickness of about 0.5 mm.

(67) The first polymer layer of the multilayer stack was a non-birefringent layer including a polymer blend comprising 80 wt % polymethyl(meth)acrylate (PMMA) (obtained under the trade designation CP-82, sold by Plaskolite, Columbus, Ohio) and 20 wt % polyvinylidene fluoride (PVDF) (obtained under the trade designation DYNEON PVDF 6008, sold by 3M Company). The second polymer layer included a polymer blend comprising 20 wt % polymethyl(meth)acrylate (PMMA) (obtained under the trade designation CP-82, sold by Plaskolite, Columbus, Ohio) and 80 wt % polyvinylidene fluoride (PVDF) (obtained under the trade designation DYNEON PVDF 6008, sold by 3M Company). The skin layers included a polymer blend comprising polyvinylidene fluoride (PVDF) (obtained under the trade designation DYNEON PVDF 6008, sold by 3M Company) and polymethyl(meth)acrylate (PMMA) (obtained under the trade designation CP-82, sold by Plaskolite, Columbus, Ohio), and further including 10 wt % of a second ultraviolet absorber (obtained under the trade designation SUKANO UV MASTERBATCH TA11-10 MB03, sold by Sukano Polymers Corporation).

(68) The hygroscopic expansion of the multilayer MOF film measured as described above is expected to be about 15 ppm per percent RH. The film weather tested as described above is not expected to exhibit tunneling after 1500 hours.

(69) All references mentioned herein are incorporated by reference.

(70) Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the present disclosure and claims are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

(71) As used in this specification and the appended claims, the singular forms a, an, and the encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this disclosure and the appended claims, the term or is generally employed in its sense including and/or unless the content clearly dictates otherwise.

(72) Various embodiments and implementation of the present disclosure are disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present disclosure can be practiced with embodiments and implementations other than those disclosed. Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments and implementations without departing from the underlying principles thereof. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows. Further, various modifications and alterations of the present invention will become apparent to those skilled in the art without departing from the spirit and scope of the present disclosure. The scope of the present application should, therefore, be determined only by the following claims.