Isolated metallic flexible back sheet for solar module encapsulation

Provided are novel back sheets for solar module encapsulation. According to various embodiments, the back sheets are ungrounded and flexible. In certain embodiments, the back sheets include an integrated flexible and electrically isolated moisture barrier. The electrically isolated moisture barrier may be a thin metallic sheet, e.g., an aluminum foil. The electrically isolated, flexible moisture barrier eliminates the need for grounding.

BACKGROUND OF THE INVENTION

Photovoltaic cells are widely used for generation of electricity, with multiple photovoltaic cells interconnected in module assemblies. Such modules may in turn be arranged in arrays and integrated into building structures or otherwise assembled to convert solar energy into electricity by the photovoltaic effect. Individual modules are encapsulated to protect the module components from the environment. A module may be framed, with the frame configured for attachment to a support surface. Framing and encapsulating materials can contribute significantly to the weight and cost of a module.

SUMMARY OF THE INVENTION

Provided are novel back sheets for solar module encapsulation. According to various embodiments, the back sheets are ungrounded and flexible. In certain embodiments, the back sheets include an integrated flexible and electrically isolated moisture barrier. The electrically isolated moisture barrier may be a thin metallic sheet, e.g., an aluminum foil. The electrically isolated, flexible moisture barrier eliminates the need for grounding.

One aspect of the invention relates to solar modules that include a transparent front layer, a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, and a back layer; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier and the moisture barrier disposed between the insulation sheet and the back layer. The back layer has dimensions greater than the moisture barrier and extends past the moisture barrier to enclose an edge of the moisture barrier.

In certain embodiments, the back layer also extends past the insulation sheet to enclose an edge of the insulation sheet. The back layer may enclose the entire perimeter edge of the moisture barrier and/or insulation sheet or a portion of the perimeter edge. All or part of a perimeter portion of the back layer may be sealed to another module component. In certain embodiments, an edge seal material surrounding the plurality of photovoltaic cells is sealed to the back layer. In certain embodiments, the insulation sheet and back layer are arranged to fully enclose the moisture barrier.

Another aspect of the invention relates to solar modules that include a transparent front layer; a multi-layer flexible back sheet; and a plurality of interconnected photovoltaic cells disposed between the transparent front layer and the multi-layer flexible back sheet. The multi-layer flexible back sheet includes an insulation sheet, an electrically isolated moisture barrier, a back layer and a seal; with the insulation sheet disposed between the plurality of photovoltaic cells and the moisture barrier, the moisture barrier disposed between the insulation sheet and the back layer, and the seal including the perimeter of the back layer and/or a bond to the perimeter of the back layer.

In certain embodiments, the seal includes a bond between the perimeter of the back layer and a second module component. The second module component may be an edge seal material that surrounds the photovoltaic cells, or may be another component. In certain embodiments, the back layer has dimensions greater than the moisture barrier and extends past the moisture barrier to cover the perimeter of the moisture barrier.

According to various embodiments, the transparent front layer may be a rigid material, e.g., a glass plate, or it may be flexible material. The photovoltaic cells may be any type of photovoltaic cells, including but not limited to CIS, CIGS, CdTe or silicon photovoltaic cells.

According to various embodiments, the moisture barrier is a pinhole free conductive material, e.g., pinhole free aluminum foil. The moisture barrier is typically thin, e.g., no more than about 50 microns thick, or no more than 25 microns thick. Other thicknesses may be used as appropriate to provide a flexible moisture barrier.

According to various embodiments, the insulation sheet is a dielectric material capable of withstanding at least a certain potential, e.g., a 600 V potential or 1000 V potential. In certain embodiments, a PET insulation sheet having a thickness of about 1-10 mils is used. The insulation sheet may be a single sheet or a multi-layer sheet, e.g., with different layers having different material properties or compositions.

The back layer may be a weatherable material capable of protecting the module from external conditions, for example polyvinyl fluoride or other fluoropolymers. In alternative embodiments, the back layer may be another material, and the module may include a weatherable material under the back layer. The back layer may be a single layer or may have multiple layers, e.g., with different layers having different material properties or compositions. If present, the bond between the back layer and another module component may be an adhesive bond, or any other type of bond sufficient to electrically isolate the moisture barrier.

Also provided are flexible multi-layer back sheets and methods of fabricating the same, as well as pre- and post-laminate back sheet and solar module stack assemblies. These and other aspects of the invention are described further below with reference to the figures.

DETAILED DESCRIPTION

Embodiments of the present invention relate to encapsulating solar modules for environmental protection and mechanical support.FIG. 1shows a not-to-scale cross-sectional view of certain components of a solar module100, including interconnected solar cells102and front and back encapsulating layers104and106, respectively. Front and back encapsulating layers104and106protect interconnected solar cells102and other module components from environmental conditions. In certain modules, a frame108surrounds the rest of the module for mechanical support.

Front and back encapsulating layers104and106can contribute significantly to the weight and transportation costs of a module. Rigid materials such as glass sheets, for example, provide good protection against environmental conditions but can add on the order of $2/sheet in transportation costs. While flexible materials such as aluminum foil are lighter and cheaper than glass, they present their own costs and issues. In particular, conventional metalized back sheets require grounding the metal in the back sheet or a grounded metal frame surrounding the module to prevent electrical shorting. Grounding a module, e.g., via a conductive frame also presents a major cost: the frame, conductors to ground, and installation costs of a grounded module are significant and present barriers to the competitive pricing of solar energy generation.

Provided herein are flexible encapsulating materials that do not require grounding or framing. The materials are considerably lighter and easier to handle than rigid encapsulation materials, and do not require the attendant issues of grounding and framing that conventional metalized encapsulation layers do. In certain embodiments, a flexible metallic back sheet is provided. Unlike current metalized back sheets for moisture impermeable solar module encapsulation, the metalized back sheets described herein do not require grounding to meet UL standards, and may be ungrounded in certain embodiments. Section 690.43 of the 2005 National Electrical Code (NEC) requires that: “Exposed non-current-carrying metal parts of module frames, equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A) regardless of voltage.” Because embodiments of the invention do not have exposed moisture barriers, or in certain embodiments, any exposed metal parts, they do not require grounding to be in compliance with the 2005 version of the US NEC. In particular embodiments, the solar modules or back sheets described herein meet the wet leakage current and/or high potential standards as defined in UL 1703. Article 690 of the 2005 NEC and UL 1703, edition 3, as revised April 2008, are incorporated by reference herein.

FIG. 2is a not-to-scale cross-sectional view of a flexible back sheet200according to certain embodiments. Back sheet200includes a flexible moisture barrier202sandwiched between an insulation sheet204and a back layer206. A seal208extends around the moisture barrier. Insulation sheet204, back layer206and seal208together electrically isolate the moisture barrier202to prevent shorting between the solar cells in the assembled module and the moisture barrier202. As is described further below with respect toFIG. 4, in certain embodiments, the back layer extends towards the front layer to cover the edges of the moisture barrier. In these embodiments, the back layer may also cover the edges of the insulation sheet.

Moisture barrier202may be any material that is flexible and moisture impermeable. Moisture impermeability may be defined by the water vapor transmission rate (WVTR), the steady state rate at which water vapor permeates through a film at specified conditions of temperature and relative humidity. According to various embodiments, the moisture barrier has a WVTR of no more than 10−2g/m2/day at 38° C. and 100% relative humidity. In certain embodiments, the moisture barrier has a WVTR of no more than 10−3g/m2/day at 38° C. and 100% relative humidity.

The moisture barrier may be a pinhole-free metallic material, including, but not limited to pinhole-free aluminum foil. In addition to aluminum or alloys thereof, metallic moisture barriers may be copper, palladium, titanium, gold, silver, iron, molybdenum, stainless steel, steel, zinc, alloys thereof such as brass, or other combinations thereof. In certain embodiments, the moisture barrier may be a metallic or other conductive material in combination with another material. The moisture barrier should be thick enough to be pinhole-free, or to meet the desired WVTR. This varies according to the particular metal used. In one example, aluminum foil as thin as about 17 microns is used. In another example, pinhole-free aluminum foil as thin as about 25 microns, or about 50 microns is used. In certain embodiments, moisture barriers between about 5 and 500 microns may be used, though other thicknesses may be used as well.

In certain embodiments, insulation sheet204is sufficient to withstand a high electrical potential between a conductive moisture barrier202and the solar cells (not shown) to prevent arcing or shorting. The voltage withstand of the sheet is a function of the material properties of the insulation sheet material as well as the thickness of the sheet. In certain examples, thickness ranges from about 1 to 10 mils or higher, though other thicknesses may be used as appropriate. According to various embodiments, the voltage withstand of the insulation sheet is at least about 500 V, at least about 600 V, at least about 700 V, at least about 800 V, at least about 900 V, at least about 1000 V, at least about 1500 V, or at least about 2000 V. In certain embodiments, the insulation material is or contains a thermoplastic material. Non-limiting examples of insulation materials include thermal polymer olefins (TPO) and non-olefin thermoplastic polymers, including polyethylene, polypropylene, polybutylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, polycarbonates, ethylene-vinyl acetate (EVA), fluoropolymers, acrylics, including poly(methyl methacrylate), or silicones, as well as multilayer laminates and co-extrusions, such as PET/EVA laminates or co-extrusions. In one example, the insulation sheet is PET. In other examples, the insulation sheet is a nylon, acylonitrile butadiene styrene ABS), polybutylene terephtalate (PBT), (polycarbonate (PC), PPS (polyphenylene sulfide (PPS), or polyphenylene oxide (PPO). Other suitable electrically insulating materials may be used, e.g., thin ceramic materials. Filled materials may also be used.

Back layer206may be a weatherable material that protects the cells and other module components from moisture, UV exposure, extreme temperatures, etc. The back layer may be a fluoropolymer, including but not limited to polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-terafluoethylene (ETFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy (PFA) and polychlorotrifluoroethane (PCTFE). Other weatherable materials may be used in addition to or instead of a fluoropolymer, including silicone polyesters, chlorine-containing materials such as polyvinyl chloride (PVC), plastisols and acrylics. In certain embodiments, any material that meets UL 1703 requirements (incorporated by reference above) is used. In one example, the back layer is PVF. In certain examples, thickness range from about 1 to about 4 mils, although other thicknesses may be used as appropriate.

Seal208includes a bond between back layer206and insulation sheet204and is effective to prevent any electrical contact between the moisture barrier and the solar cells or any other component of the module at the edge of moisture barrier202. It is typically a permanent or irreversible seal and prevents peeling at the edges that would expose the edge of moisture barrier202. According to various embodiments, the seal is at least 0.5 mm, 1 mm or 2 mm wide and extends around the edge of the moisture barrier. The bond between back layer206and insulation sheet204may be an adhesive bonding, a fusion bonding, a welding, a solder bond, or a mechanical fastening. As used herein, the term “permanent seal” refers to a seal that has a resistance to rupture greater than a frangible seal. As used herein, “irreversible seal” refers to seal that is unbreakable by exposure to atmospheric heat and weather conditions, and generally must be deliberately tampered with to be broken. In certain embodiments, the seal includes covalent bonding, e.g., between an adhesive and the back layer and/or insulation sheet, or between the insulation sheet and back layer, etc.

If an adhesive material is used, it may be a thermoplastic adhesive, a liquid adhesive, a curable adhesive, or any other type of adhesive that creates an irreversible seal, is resistant to peeling and has good moisture resistance. Thermoplastic adhesives that may be used include acrylics, silicone resins, polyamines and polyurethanes. In certain embodiments, the adhesive may also be used to adhere the insulation sheet and back layer to the moisture barrier. In certain embodiments, one of the layers may be formed by extrusion coating or casting, e.g., on a chemically primed surface. For example, moisture barrier202may be adhered to insulation sheet204. Insulation sheet204or (insulation sheet204and moisture barrier202) may then be chemically primed and back layer206formed by extrusion coating or casting onto the chemically primed surface.

FIG. 3shows an example of solar module300having a metalized back sheet322as described above with reference toFIG. 2. For the purposes of illustration, the schematic is not drawn to scale. Solar cells318may be any type of solar cells, including but not limited to, semiconductor-based solar cells including microcrystalline or amorphous silicon, cadmium telluride, copper indium gallium selenide or copper indium selenide, dye-sensitized solar cells, and organic polymer solar cells.

Solar cells318are encapsulated by a material310that protects the solar cells and that may include one or more layers of a thermoplastic material, e.g., an acrylic or silicone material. A material314surrounds solar cells318. The material314may be an organic or inorganic material that has a low inherent WVTR (typically less than 1-2 g/m2/day) and, in certain embodiments may absorb moisture, prevents its incursion through and along edges of material310. In one example, a butyl-rubber containing moisture getter or desiccant is used. The encapsulated cells318are protected by a transparent front layer312and back sheet322, including weatherable back layer306, insulation sheet304, moisture barrier302and seal308.

In the figure, moisture barrier material302is disposed under solar cells318, but extends at least a small distance past solar cells318, such that it partially underlies material314. In certain embodiments, the outer perimeter of the moisture barrier302is located between the inner and outer perimeters of the material314.

FIG. 4depicts a photovoltaic module400including a multi-layer back sheet422according to another embodiment. For the purposes of illustration, the schematic is not drawn to scale. As described above, solar cells418are encapsulated by a material410. A material414surrounds the solar cells to provide an edge seal. The encapsulated cells418are protected by a transparent front layer412and multi-layer back sheet422. Multi-layer back sheet422includes moisture barrier402disposed between insulation sheet404and back layer406. Back layer406has planar dimensions larger than those of the moisture barrier402and insulation sheet404. The perimeter portion416of back layer406extends toward front layer412so that back layer406covers the perimeter edge442of moisture barrier402as well as surface432of moisture barrier402. In the figure, the perimeter portion416of back layer406covers the perimeter edge444of insulation sheet404as well. The back layer406may or may not physically contact each of the edges442and444of the moisture barrier and insulation sheet, respectively.

In this example, perimeter portion416of back layer406is bonded to edge material414to form a seal at408. Depending on the particular arrangement of the module components, the perimeter portion416of back layer406may be sealed to any suitable materials or layers that are disposed on the opposite side of moisture barrier402as the main portion of back layer406. For example, the back layer may form a seal with an insulation sheet, an encapsulant material such as material410, a transparent front layer412, or any other suitable module component, or combination of these. According to various embodiments, the seal is at least 0.5 mm, 1 mm or 2 mm wide. It may extend around the module to fully isolate the moisture barrier.

Prior to being folded or bent toward the photovoltaic cells, the back layer406may have dimensions slightly larger than the front layer412, i.e., to account for the perimeter portion416that is bent toward the edge material. According to various embodiments, the back layer extends up to 10 mm past each edge of the moisture barrier and/or insulation sheet. In certain embodiments, the insulation sheet and moisture barrier are about equally sized. In other embodiments, the insulation sheet may be larger than the moisture barrier.

As indicated above, in certain embodiments, the module includes a permanent and/or irreversible seal that includes bonding between the back layer and the edge material or other module component to which the back layer is sealed. This may be an adhesive bonding, a fusion bonding, a welding, a solder bond, or a mechanical fastening. In certain embodiments, the seal includes covalent bonding, e.g., between an adhesive and the back layer and/or edge material, or between the back layer and edge material, etc. Moisture barrier402is electrically isolated by insulation sheet404and sealed back layer406.

In certain embodiments, the moisture barrier overlaps with an edge seal material surrounding the solar cells in a plane vertical to the module.FIG. 5shows a plan view550of solar cell area518and material514surrounding solar cell area518according to certain embodiments. Also shown is a view551of a metallic moisture barrier502overlying a back layer, the perimeter portion516of which is shown. (For the purpose of illustration, other layers, such as an insulation sheet and encapsulation material, etc. are not depicted.)

Plan view552shows the solar cell area518and surrounding material514(as depicted in view550) overlying the metallic moisture barrier502and the back layer including the perimeter portion516(as depicted in view551). Material514and metallic moisture barrier502overlap in region536. This provides moisture protection over the entire solar cell area518. All or a portion of the back layer that extends past the moisture barrier (perimeter area516) may contact and/or be sealed to all or a portion of another module component, e.g., to an insulation sheet (as depicted inFIG. 3), edge material514(as depicted inFIG. 4), or other appropriate layer or material. In certain embodiments, the perimeter portion of the back layer may contact or be sealed to multiple other layers or materials in the module.

Conventional back sheets that incorporate a metallic sheet, such as Tedlar®/Al foil/PET back sheets, require grounding the aluminum foil in the back sheet or a grounded metal frame surrounding the module to meet UL and other safety requirements. This is due to the exposure or possible exposure of the aluminum foil at the cut edge. According to various embodiments, the moisture barriers described herein are ungrounded. The overlying and underlying polymers layers (e.g., PET insulation sheet and PVF weatherable back layer) together with the seal surrounding the moisture barrier electrically isolate the moisture barrier, obviating the need to ground the moisture barrier. Because the electrically isolated moisture barriers described herein do not need to be grounded, mechanical support considerations are decoupled from electrical considerations. Thus, according to various embodiments, the solar cell modules described herein included frameless as well as framed modules. In certain embodiments, the unframed modules may be configured to be attached an array frame or other support structure at an installation site.

Also provided are processes of fabricating the multi-layer back sheets described herein.

FIGS. 6-8depicts operations in roll-to-roll processes of forming multi-layer back sheets according to various embodiments.FIGS. 6 and 7depict operations in forming multi-layer back sheets as depicted inFIG. 3andFIG. 8depict operations in forming multi-layer back sheets as depicted inFIG. 4.

Turning first toFIG. 6, in process600, discrete sheets of metal foil, typically having dimensions less than the underlying back layer and overlying insulation sheet are inserted into a pre-laminate stack including a polymeric insulation sheet and back layer material. The process begins at an operation602, in which insulation sheet and back layer polymers and, if used, thermoplastic adhesives are provided on webs. For example, webs of PET, adhesive and PVF may be provided to assemble a PET/adhesive/adhesive/PVF pre-laminate stack. In an operation604, discrete sheets of a metallic moisture barrier are inserted between the polymer sheets. For example, a sheet of aluminum foil is inserted between adhesive sheets to form a PET/adhesive/Al foil/adhesive/PVF pre-laminate stack assembly. The aluminum foil or other moisture barrier may be inserted before or after transverse cuts are made to form module-sized stacks. The pre-laminate stack assembly including a moisture barrier is then laminated in an operation606, forming a seal around the entire perimeter of the moisture barrier. If still on a roll, the laminate stack may be cut as appropriate to define a module back sheet in an operation608. The laminate stack may then be assembled with the solar cells, front layer and other module components to complete the module. One of skill in the art will understand that the order of various cutting, laminating and module assembly operations may vary. Also, another type of bonding (welding, fusing, etc.) may be performed form the seal surrounding the moisture barrier.

In process650, rather than inserting discrete sheets, the aluminum or other moisture barrier material is also provided as a web. The process begins in an operation652in which the polymer insulation sheet, adhesives (is used), backing layer and moisture barrier are provided on webs to form a pre-laminate stack assembly, e.g., insulation sheet/adhesive/moisture barrier/adhesive/back layer. In certain embodiments, the width of the moisture barrier web is less than the other webs to allow for formation of a seal. The pre-laminate stack assembly is laminated in an operation654. The laminate stack is cut in an operation656to form module-sized laminate stacks. In certain embodiments, the resulting module-sized stack includes a moisture barrier material extending to the cut edges. This is depicted inFIG. 7, which shows a top view of laminate stack702, including moisture barrier704, uncut edges708aand708b, cut edges710aand710b, and a seal706along opposing uncut edges708aand708bof the laminate stack. Seal706includes bonded-together insulation sheet and backing layer polymeric layers. The moisture barrier704and the overlying and underlying polymer layers are coextensive along the length of module-sized stack (direction “Y” in the figure). A side view of a cut edge711is shown, with polymer layers712and714and moisture barrier704. (Adhesive layers are not depicted for the sake of illustration.). Returning toFIG. 6, to electrically isolate the moisture barrier, the cut edges are folded in an operation658. An example of such as fold is depicted at716inFIG. 7, with polymer layers712and714and moisture barrier704curved inward together, such that the edge of moisture barrier704is fully isolated by one or more of layers712and714. An additional sealing operation may then be performed, e.g., by applying heat, pressure and or adhesive to the fold. The fold may include one or more inward curved portions, including bent or angled portions. In the example shown inFIG. 7, the edge is folded twice to form two inward curved portions, fully isolating the edge of the moisture barrier along the cut sides. The fold may be considered part of the seal that extends around the solar module.

FIG. 8depicts operations in roll-to-roll processes of forming a multi-layer back sheet such as that depicted inFIG. 4. In process800, the insulation sheet and metal foil are cut together, to form discrete insulation sheet/metal barrier stacks that sized and positioned on the back layer material such that the perimeter of the back layer extends around the metal barrier and insulation sheet. The process begins at an operation802, in which insulation sheet and moisture barrier materials are provided. If used, thermoplastic or other adhesives may also be provided. The materials may be provided on webs or in other appropriate form. In an operation804, the overlying polymer and moisture barrier material are cut to form discrete stacks of insulation sheet and moisture barrier material in their desired size. In embodiments in which the insulation sheet and moisture barrier are of approximately the same size, the insulation sheet and moisture barrier may be cut simultaneously. Also, in certain embodiments, the insulation sheet material and moisture barrier material may be received already appropriately sized without needing to be cut. Once an appropriately-sized insulation sheet and moisture barrier stack is formed, it is then positioned on back layer material in an operation806. Adhesive layers may also be part of the stack or otherwise appropriately placed. The back layer material may be provided on a web. A lamination operation may be performed to bond the layers together in an operation808. If still on a roll, the back layer may be cut as appropriate to define a module back sheet in an operation810. At this point, the insulation sheet covers one surface of the moisture barrier with the back layer covering the opposite surface of the moisture barrier. The perimeter of the back layer may be bent or otherwise extended upward to cover the edge of moisture barrier, or this may occur during further processing when the back sheet is assembled with the rest of the module components. For example, the back layer/moisture barrier/insulation sheet stack may then be assembled with the solar cells, front layer and other module components to complete the module. In doing so, the perimeter of the back layer may be sealed in an operation812to another module component, such as the edge seal material that surrounds the solar cells. One of skill in the art will understand that the order of various cutting, laminating and module assembly operations may vary.

In a process850, rather than positioning discrete stacks of insulation sheet and moisture barrier material on the back layer, the flexible back sheets may be assembled using a roll-to-roll process. The process begins in an operation852in which the polymer insulation sheet, adhesives (is used), backing layer and moisture barrier are provided on webs to form a pre-laminate stack assembly, e.g., insulation sheet/adhesive/moisture barrier/adhesive/back layer. In certain embodiments, the width of the back layer web is greater than the insulation sheet and moisture barrier webs to allow the perimeter of the back layer to cover the edges of those layers. The pre-laminate stack assembly is laminated in an operation854. The laminate stack is cut in an operation856to form module-sized laminate stacks. In this case, the laminate stacks may look like the laminate stack shown at view702inFIG. 7, with706representing the width of the back layer material that extends past the insulation sheet and moisture barrier on the uncut edges. As depicted at view711inFIG. 7, the resulting module-sized stack includes a moisture barrier material extending to the cut edges. To electrically isolate the moisture barrier, the cut edges are folded in an operation858, as depicted at716inFIG. 7. The unfolded edges of the back layer may then be sealed to another module component as described above in an operation860. In certain embodiments, the folded edges may be similarly sealed.

Other Embodiments

According to various embodiments, the flexible back sheet may include one or more additional layers. For example, in certain embodiments, additional layers may be between the moisture barrier layer and a weatherable material and/or between the moisture barrier layer and an insulation layer. The seal may include a bond between any of the layers, so long as a layer overlying the moisture barrier is bonded to an underlying barrier such to prevent any electrical connection to the edge of the moisture barrier.

While the description above refers chiefly to metallic moisture barriers, other types of flexible moisture barriers are within the scope of the invention, including moisture barriers made of non-metallic conductive materials, semiconductor materials, etc. As described above, in certain embodiments, the back sheets and methods described herein find particular application with conductive moisture barriers.

In addition to the specific examples of polymeric materials that may be used for the insulation sheet, back layer, adhesives, etc., examples of materials that may be used as appropriate for one of these layers or for other layers in the module include, silicone, silicone gel, epoxy, RTV silicone rubber, polydimethyl siloxane (PDMS), polyvinyl butyral (PVB), polycarbonates, acrylics, urethanes including thermoplastic polyurethanes (TPU), poly(vinyl acetal), polyolefin block elastomers, ethylene acrylate ester copolymers, acid copolymers, silicone elastomers, epoxy resins, polyolefin block elastomers, ethylene acrylate ester copolymers, rubber, thermoplastic elastomers, other materials with similar material properties, and mixtures thereof.

Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the invention. It should be noted that there are many alternative ways of implementing both the processes and apparatuses of the present invention. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein.