WO2012140585A1 - Encapsulating polymeric multilayer film for cells for photovoltaic modules, and protective integrated sheet, of the type of a backsheet or frontsheet, comprising such film - Google Patents

Encapsulating polymeric multilayer film for cells for photovoltaic modules, and protective integrated sheet, of the type of a backsheet or frontsheet, comprising such film Download PDF

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Publication number
WO2012140585A1
WO2012140585A1 PCT/IB2012/051781 IB2012051781W WO2012140585A1 WO 2012140585 A1 WO2012140585 A1 WO 2012140585A1 IB 2012051781 W IB2012051781 W IB 2012051781W WO 2012140585 A1 WO2012140585 A1 WO 2012140585A1
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Prior art keywords
layer
multilayer film
film according
adhesive
encapsulating
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PCT/IB2012/051781
Other languages
French (fr)
Inventor
Filippo MAGRIN
Michele DETASSIS
Original Assignee
M.G. Lavorazione Materie Plastiche S.P.A.
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Publication of WO2012140585A1 publication Critical patent/WO2012140585A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B32B17/06—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material
    • B32B17/10—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin
    • B32B17/10005—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing
    • B32B17/1055—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer
    • B32B17/10743—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer containing acrylate (co)polymers or salts thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B32B17/06—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material
    • B32B17/10—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin
    • B32B17/10005—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing
    • B32B17/1055—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer
    • B32B17/10788—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material of synthetic resin laminated safety glass or glazing characterized by the resin layer, i.e. interlayer containing ethylene vinylacetate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/048—Encapsulation of modules
    • H01L31/049—Protective back sheets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/20—Light-sensitive devices
    • H01G9/2068—Panels or arrays of photoelectrochemical cells, e.g. photovoltaic modules based on photoelectrochemical cells
    • H01G9/2077—Sealing arrangements, e.g. to prevent the leakage of the electrolyte
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/80—Constructional details
    • H10K30/88—Passivation; Containers; Encapsulations
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to an encapsulating polymeric multilayer film for cells for photovoltaic modules.
  • the present invention also relates to an integrated protective sheet, of the so-called backsheet or frontsheet type, which comprises a polymeric multilayer film according to the invention.
  • the typical structure of a first-generation photovoltaic module with crystalline silicon cells is constituted by the following main components: a glass sheet, a first upper encapsulating film, the photovoltaic cells interconnected by the electrical connection strips, a second lower encapsulating film, and a lower and generally laminated multilayer protective sheet, known in the jargon as backsheet.
  • the glass sheet is replaced with a protective laminated sheet, known in the jargon as frontsheet.
  • the typical structure normally comprises the following layers: a glass sheet, the photovoltaic cell deposited as thin film on the glass, a lower encapsulating film, another glass sheet or a protective laminated sheet, i.e., the backsheet.
  • An alternative structure for the second-generation photovoltaic modules is the following: a frontsheet, i.e., a protective sheet made of ETFE (ethylene tetrafluoroethylene) or other protective transparent laminated element, an encapsulating film, arranged above, the photovoltaic cell deposited as thin film, on a lower sheet of metal or polymeric material.
  • a frontsheet i.e., a protective sheet made of ETFE (ethylene tetrafluoroethylene) or other protective transparent laminated element
  • ETFE ethylene tetrafluoroethylene
  • encapsulating film arranged above, the photovoltaic cell deposited as thin film, on a lower sheet of metal or polymeric material.
  • Third-generation modules are currently also known but have only a limited diffusion; they have photoelectrochemical cells, for example Gratzel cells, or semiconducting polymers, for example cells with bulk heterojunctions, the typical structure of which is as follows: a protective upper encapsulating film which acts as a barrier against oxygen and humidity, a photovoltaic cell of the electrochemical type or with semiconducting polymers, a lower protective encapsulating film acting as a barrier against oxygen and humidity.
  • photoelectrochemical cells for example Gratzel cells
  • semiconducting polymers for example cells with bulk heterojunctions
  • a photovoltaic module consists in the manual or automated assembly of the various component layers and their discontinuous or continuous lamination with a process which typically provides for the application of heat and pressure.
  • the encapsulating film in all of the above cited manufacturing solutions, with lamination is required to undergo deformation when hot in order to incorporate the cells, binding the upper and lower protective layers and thus forming the protective enclosure which, through the years, protects the electronics, i.e., the cells and the connections, against atmospheric attacks: humidity, solar radiation, particularly UV rays, hail, frost, pollutant atmospheric agents, etc.
  • Humidity microbubbles are due to the condensation that is present on the surfaces of the components, in particular between the encapsulating film and the backsheet.
  • microbubbles cause a series of functional problems as well as aesthetic ones, among which the most important are the reduction of the electrical insulation of the cell by accumulation of humidity therein and the reduction of the energy conversion efficiency of the photovoltaic module due to the reduced optical transmittance.
  • the delamination of the module between the encapsulating film and the protective backsheet or frontsheet is caused by the poor adhesion between the encapsulating film and the protective sheet.
  • This situation of poor adhesion can be ascribed to the migration and accumulation of humidity or other substances in the region of interface between the encapsulating film and the protective sheet and to the predominantly thermal stresses to which the photovoltaic module is subjected during its life.
  • the surface between the encapsulating film and the protective sheet is normally contaminated by small impurities such as dust, organic deposits and others, caused by the production process.
  • Another drawback of the background art is due to the fact that the production process provides for the handling of each individual component of the module.
  • the module production line requires a machine that unwinds and cuts the encapsulating film and an adapted separate machine that unwinds and cuts the protective film.
  • each component including the encapsulating film and the protective backsheet or frontsheet, must be positioned precisely and carefully onto each other.
  • One currently known method for increasing the quality of the photovoltaic module while reducing production costs is to integrate the protective backsheet or frontsheet with the encapsulating film.
  • a first method provides for simply resting the encapsulating film on the protective sheet, optionally with a gentle application of pressure and heat so as to provide a pre-laminated element which comprises these two layers.
  • a second method provides for coupling by lamination with adhesive.
  • a third method provides for coupling by extrusion lamination.
  • a fourth method provides for the spreading of the encapsulating film on the protective sheet (extrusion coating).
  • the method by simple resting contact does not solve the problem of microbubbles or the drawback of the risk of delamination.
  • the method of coupling by lamination with adhesive entails limitations and risks linked to the possible interactions among components of the encapsulating film and particularly the peroxides and silanes, with the components of the adhesive, in particular in relation to the durability of the photovoltaic module.
  • the method of coupling by extrusion lamination does not solve the problem of limited adhesion, i.e., of delamination risks.
  • the method of coating the encapsulating film on the protective film also has the problem of limited adhesion with risk of delamination.
  • lamination between the encapsulating film, which is extremely elastic, and the protective sheet, which is typically rigid or semirigid, can entail defects such as creases, wrinkles and small air bubbles which remain trapped in the lamination.
  • a standard encapsulating film is usually based on EVA, and peroxides and silanes must be present in its formulation.
  • the peroxides are necessary because the film of EVA as such, being a thermoplastic material with a low melting point (approximately 60-70°C), cannot withstand the operating temperatures (where sometimes the photovoltaic modules reach temperatures of even 60-70°C and in any case are typically tested up to 85°C).
  • the peroxides during the lamination of the module (hot, typically at the temperature of approximately 150°C for a time of approximately 15 min) break down, trigger the cross-linking of the EVA polymer and trigger the linking of the silane molecules to the molecular chain of the EVA polymer.
  • Silanes are instead necessary to improve the adhesion of the encapsulating EVA film to the glass and in general to polar surfaces (such as those of the cells and of the electrical contacts).
  • silanes react with the polar surfaces, developing a very strong chemical bond which is stable even in the presence of humidity.
  • EVA is a polar material with a certain affinity for water
  • water can accumulate and permeate the EVA, reaching over time the surface between the glass and the encapsulating element. Here it becomes interposed between the EVA and the glass, reducing mutual adhesion drastically.
  • the EVA film maintains its adhesion with respect to the cited surfaces even in the presence of humidity which, due to prolonged exposure to bad weather, can always accumulate within the photovoltaic module.
  • Peroxides are highly aggressive substances which have a low molecular weight and therefore migrate easily in the encapsulating film. Peroxides can therefore migrate over time until they reach the layer of adhesive that indeed binds the encapsulating film to the protective frontsheet or backsheet.
  • the photovoltaic module which is always exposed to the inclemency of the weather, delaminates in the region between the encapsulating element and the backsheet and/or frontsheet, thus inducing regions of accumulation of humidity and air, and this leads to partial or total damage to the module, with loss of electrical insulation, loss of conversion efficiency, et cetera.
  • silanes too, can likewise reduce partly the performance of the adhesive, since after migration they can react with the adhesive and can reduce its ability to cross-link and bind to the surfaces of the encapsulating element from one side of the frontsheet and/or backsheet from the other.
  • the aim of the present invention is to provide an encapsulating polymeric multilayer film for cells of photovoltaic modules which makes it possible to encapsulate a photovoltaic cell without the drawbacks cited above.
  • an object of the invention is to provide an encapsulating polymeric multilayer film that can be coupled to a protective frontsheet or backsheet film safely and durably.
  • Another object of the invention is to provide an encapsulating polymeric multilayer film which can be coupled to a protective sheet with methods of a known type.
  • a further object of the invention is to provide an encapsulating polymeric multilayer film which is capable of improving the durability of a photovoltaic module to which it belongs by reducing the risks of delamination and of microbubbles.
  • Another object of the invention is to provide an encapsulating polymeric multilayer film that accordingly makes it possible to devise a process for the production of photovoltaic modules which is simpler and cheaper than known ones.
  • Another object of the invention is to devise an integrated protective backsheet or frontsheet of the integrated type, which comprises an encapsulating film according to the same invention.
  • Another object of the invention is to propose an encapsulating polymeric multilayer film for cells of photovoltaic modules and an integrated protective backsheet or frontsheet comprising said film which can be manufactured with known systems and technologies.
  • an encapsulating polymeric multilayer film for cells for photovoltaic modules to be integrated by lamination with adhesive with a protective sheet, backsheet or frontsheet, for photovoltaic cells of a photovoltaic module, characterized in that it comprises
  • Figure 1 is a schematic sectional view of a multilayer film according to the invention in a first embodiment thereof;
  • Figure 2 is a schematic sectional view of a multilayer film according to the invention in a second embodiment thereof;
  • Figure 3 is a schematic sectional view of a multilayer film according to the invention in a third embodiment thereof;
  • Figure 4 is a schematic sectional view of an integrated protective sheet according to the invention;
  • Figure 5 is a schematic sectional view of a second embodiment of an integrated protective sheet according to the invention.
  • an encapsulating polymeric multilayer film for cells for photovoltaic modules according to the invention is generally designated by the reference numeral 10.
  • the multilayer film 10 is intended to be integrated by lamination with adhesive 1 1 with a protective backsheet or frontsheet 12 for the photovoltaic cells of a photovoltaic module.
  • the multilayer film 10 comprises:
  • the second layer 14 has no additives that can compromise adhesion and its durability and in particular is free from residual peroxides, non- linked silanes, slip agents, and the like.
  • the second layer 14 also acts as a barrier against the migration of these substances, i.e., silanes and peroxides, from the first layer 13 toward the adhesive layer 1 1 , and also acts as a barrier against the passage of any residues of solvent or of not cross-linked adhesive from the adhesive layer 1 1 toward the first layer 13.
  • these substances i.e., silanes and peroxides
  • the second layer 14 is composed of a polymer with high resistance to deformation when heated (creep) and to the migration of peroxides and silanes.
  • Creep resistance is important because the photovoltaic module, in the conditions for use and testing, is subjected to high temperatures, as indicated above, and at these temperatures it is necessary to ensure that the cells cannot move, overlap or tension the electrical connections or even detach from them.
  • the second layer 14 comprises a semicrystalline thermoplastic polymer whose melting point is higher than 85°C and preferably higher than 95°C.
  • a semicrystalline thermoplastic polymer with these characteristics achieves the aim of contrasting the migration of silanes and peroxides from the first layer 13, through the second layer 14, toward the adhesive layer 1 1.
  • thermoplastic polymer As the crystallinity of the thermoplastic polymer increases, it opposes increasingly the migration of permeating agents, i.e., silanes and peroxides, which on the contrary diffuse well in the amorphous phase and very poorly in the crystalline phase.
  • permeating agents i.e., silanes and peroxides
  • each crystalline phase is characterized by a typical melting point, and since in general the higher the crystalline phase and the higher the melting point of the material (as detected by the melting peak of the classical calorimetric differential thermal analysis (DSC)), in order to limit and if possible prevent permeation it is necessary to use semicrystalline polymers with the highest possible melting point, certainly higher than the operating conditions.
  • DSC classical calorimetric differential thermal analysis
  • the semicrystalline thermoplastic polymer is present in the second layer 14 in a percentage between 40% and 100%, preferably between 60% and 100%, and in particular 100%.
  • thermoplastic polymer If the semicrystalline thermoplastic polymer is not present in the percentage of 100%, the remaining percentage is to be understood as being constituted by other thermoplastic polymers.
  • the second layer 14 has a thickness comprised between 1 and 400 ⁇ , preferably between 50 and 150 ⁇ , and in particular between 75 and 125 ⁇ .
  • the semicrystalline thermoplastic polymer present in the second layer 14 is constituted by a polymer chosen among: low-density polyethylene (LDPE), low-density linear polyethylene (LLDPE), high- density polyethylene (HDPE), and other similar and equivalent materials, or, as an alternative, by polar copolymers of ethylene, such as ethyl vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethyl butyl acrylate (EBA), and other similar and equivalent materials.
  • LDPE low-density polyethylene
  • LLDPE low-density linear polyethylene
  • HDPE high- density polyethylene
  • EVA ethyl vinyl acetate
  • EMA ethylene methyl acrylate
  • EBA ethyl butyl acrylate
  • the semicrystalline thermoplastic polymer present in the second layer 14 is constituted by EVA with a vinyl acetate content of less than 20%, preferably less than 10% and in particular less than 6%, with a melt flow rate of less than 50 g/10 min, preferably less than 20 g/10 min and in particular less than 5 g/10 min, the melt flow index being understood as measured at 190 °C and with 2.16 kg of thrust.
  • the cited semicrystalline thermoplastic polymers with these characteristics have a substantially apolar chemical structure (LDPE, LLDPE, HDPE) or a weakly polar one (EVA) and since the potential migrating substances are all polar, this further limits their migration.
  • LDPE substantially apolar chemical structure
  • LLDPE low density polyethylene
  • HDPE high density polyethylene
  • EVA weakly polar one
  • the second layer 14 can receive the addition of mineral fillers, such as calcium carbonate, talc, aluminum trihydroxide, titanium dioxide and the like, or organic fillers, such as carbon black, which are adapted to give high resistance to creep.
  • mineral fillers such as calcium carbonate, talc, aluminum trihydroxide, titanium dioxide and the like
  • organic fillers such as carbon black
  • the second layer 14 Since the second layer 14 has no peroxides, it must nonetheless be able to provide high resistance to creep.
  • the mineral fillers are preferably comprised in a percentage between 1% and 60%, and particularly between 10% and 40%.
  • the outer face of the second layer 14 is preset for lamination operations by means of per se known pretreatment techniques, such as corona treatment, flame treatment, plasma treatment, priming and the like.
  • the second layer 14 can have UV and thermal stabilizing additives, such as for example UV stabilizers of the family of sterically hindered amines (HALS), such as for example TINUVIN® 770 of the BASF company, UV absorbers (UVA) of the benzophenone family, for example CYASORB® UV-531 by the Cytech company, or benzotriazoles, for example TINUVIN® 326 of the BASF company, or thermal stabilizers, such as for example IRGAFOS® 168 of the BASF company.
  • UV stabilizers of the family of sterically hindered amines (HALS) such as for example TINUVIN® 770 of the BASF company
  • UV absorbers (UVA) of the benzophenone family for example CYASORB® UV-531 by the Cytech company
  • the second layer 14 also acts as a barrier against humidity, thanks to a water vapor permeability (WVTR) of less than 25 g/m 2 per day, preferably less than 5 g/m 2 per day, measured at 23°C and 85/15 RH.
  • WVTR water vapor permeability
  • the second layer 14 has stiffness properties adapted to facilitate the workability of the film 10, by means of a traction elasticity modulus (Young's modulus) of more than 50 MPa and preferably more than 100 MPa.
  • a traction elasticity modulus Young's modulus
  • the second layer 14 comprises an amorphous thermoplastic polymer, not a semicrystalline one, whose glass transition temperature is higher than 85°C and preferably higher than 105°C.
  • a similar second layer 14 is composed of a polymer with additives adapted to cross-link by heat or humidity or another technique such as irradiation with gamma rays and the like, prior to lamination of the photovoltaic module.
  • - silane compounds adapted to link, by means of peroxides, during an operation of extrusion of the second layer 14, to the molecular chains of the polymer of the second layer, or already linked to the molecular chain of the polymer of the second layer 14, adapted to allow the cross-linking of the layer 13 due to humidity and optionally also to the heat prior to the production of the photovoltaic module for which the film 10 is intended.
  • the multilayer film 10 can comprise pigments and colors adapted to give the desired color of the integrated backsheet that incorporates it.
  • the first layer 13 is composed of a thermoplastic polymer that contains cross-linking agents.
  • thermoplastic polymer that defines the first layer 13 is EVA, for example of the type of Elvax 150W by the Dupont company.
  • the first layer 13 receives the addition of cross-linking agents such as peroxides, binding agents such as silanes, and UV and thermal stabilizing additives.
  • the peroxides are organic peroxides, for example of the peroxycarbonate family, for example LUPEROX TBEX of the ARKEMA company.
  • the bonding agents are for example organic silanes, for example of the family of methacryloxypropyltrimethoxysilanes (MTMSI), for example Z-6030 of the Dow Corning company.
  • MTMSI methacryloxypropyltrimethoxysilanes
  • the UV stabilizing agents are constituted by sterically hindered amines (HALS), for example TINUVIN® 770 by the BASF company, UV absorbers (UVA) of the benzophenone family, such as CYASORB UV-531 of the CYTECH company, or benzotriazoles such as TINUVIN® 326 of the BASF company, and thermal stabilizers such as IRGAFOS® 168 of the BASF company.
  • HALS sterically hindered amines
  • UVA UV absorbers
  • benzophenone family such as CYASORB UV-531 of the CYTECH company
  • benzotriazoles such as TINUVIN® 326 of the BASF company
  • thermal stabilizers such as IRGAFOS® 168 of the BASF company.
  • the thickness of the first layer 13 is comprised between 50 and 1000 ⁇ and is preferably comprised between 250 and 500 ⁇ .
  • the first layer 13 can be constituted by a mixture of predominantly amorphous thermoplastic polymer as described above and other thermoplastic polymers.
  • the predominantly amorphous thermoplastic polymer is present in a percentage between 40% and 100%, more preferably is present in a percentage between 60% and 100%, and in particular is present as 100%.
  • the first layer 13 is based on a thermoplastic polymer without cross-linking agents, such as for example ethylene methacrylate (EMA).
  • EMA ethylene methacrylate
  • the first layer 13 comprises low-density linear polyethylene (LLPDE) and additives such as silanes which are adapted to cross-link due to humidity or other known method during the lamination of the photovoltaic module.
  • LLPDE low-density linear polyethylene
  • additives such as silanes which are adapted to cross-link due to humidity or other known method during the lamination of the photovoltaic module.
  • the encapsulating polymeric multilayer film 1 10 comprises a third layer 1 15, which acts as a binder and is intermediate between the first layer 1 13 and the second layer 1 14, with the second layer 1 14 in contact with the adhesive 1 1 1 , for connection to a generic protective sheet 1 12.
  • the third layer 1 15 is composed of a mixture of polymers which are present in the first layer 1 13 and in the second layer 1 14.
  • the third layer 1 15 is constituted by binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA) and the like, or by a mixture of the polymers that are present in the first layer 113 and in the second layer 1 14 with the binding polymers.
  • binding polymers such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA) and the like, or by a mixture of the polymers that are present in the first layer 113 and in the second layer 1 14 with the binding polymers.
  • the encapsulating polymeric multilayer film 210 comprises a third intermediate barrier layer 215, which is joined to the first layer 213 by means of a fourth layer 216 which acts as a binder, and is joined to the second layer 214 by means of a fifth layer 217 which acts as a binder.
  • the third layer 215 is constituted for example by an oxygen barrier polymer, such as ethylene vinyl alcohol (EVOH), polyamide (PA), and the like, while the fourth layer 216 and the fifth layer 217 are made of binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA), and the like.
  • an oxygen barrier polymer such as ethylene vinyl alcohol (EVOH), polyamide (PA), and the like
  • PA polyamide
  • binding polymers such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA), and the like.
  • the adhesive layer 1 1 , 1 1 1, 21 1 is of a type chosen among polyurethane adhesives, polyester adhesives, epoxy adhesives, and the like, and for example is constituted by a two-part solvent-based polyurethane adhesive.
  • the film 10 according to the invention is characterized in that the first and second layers are coupled by means of a coextrusion process.
  • first and second layers are coupled by means of a process of extrusion coating of the first layer on the second layer.
  • the first and second layers are coupled by means of a simple resting contact process.
  • first and second layers can be coupled by means of a process of lamination with extrusion.
  • the film 10 can be supplied to the coupling with the protective sheet 12 in turn with a protective sheet or liner, to avoid transfer into the reel of peroxides and silanes, for example a sheet of high-density polyethylene (HDPE).
  • a protective sheet or liner to avoid transfer into the reel of peroxides and silanes, for example a sheet of high-density polyethylene (HDPE).
  • HDPE high-density polyethylene
  • the present invention also relates to a protective sheet, designated in
  • FIG. 318 of the backsheet or frontsheet type, which is integrated with an encapsulating polymeric layer, for the protection of cells of photovoltaic modules.
  • the integrated protective sheet 318 has a protective film 312 which comprises a first layer of PET (polyethylene terephthalate) 319, which is external, and a second layer of PET 320, which is internal, interlaid by a layer of adhesive 321 , and is intended to be used as a backsheet.
  • a protective film 312 which comprises a first layer of PET (polyethylene terephthalate) 319, which is external, and a second layer of PET 320, which is internal, interlaid by a layer of adhesive 321 , and is intended to be used as a backsheet.
  • the background art instead normally provides for a protective backsheet to comprise three layers, for example a first layer of PET, a second layer of PET, and a third binding layer where the coupling layer can be EVA, PA, an ionomer, and the like.
  • a further example of three-layer backsheet comprises a first layer of PVF (known as "Tedlar”, by the DuPont company, which is mostly used), a second layer of PET, and a third layer again made of PVF.
  • the cited layers of the two examples of backsheet are typically coupled by means of adhesive (polyester-based, polyurethane based, but not only).
  • the integrated protective sheet 318 of the backsheet type, therefore has a protective sheet 312 which lacks the third sealing layer and only has the two layers 319 and 320 made of PET.
  • This solution frees a backsheet manufacturer from the need to manufacture products with a sealing layer that must be different for each different class of encapsulating layer, since joining occurs by means of an adhesive layer 311 as described above and the adhesive layer 31 1 is protected by the second layer 14 of the encapsulating multilayer film 10, 1 10 and 210 according to the invention as described above.
  • the integrated protective sheet 318 offers better quality, understood as defect reduction, since with the second layer 14 that acts also as an agent for coupling to the encapsulating layer there is one less surface and therefore a smaller risk of condensation and various contaminations.
  • the integrated protective sheet 418 has a protective film 412 which comprises an outer layer 419 made of EFTE (ethylene tetrafluoroethylene) and a layer of adhesive 420.
  • EFTE ethylene tetrafluoroethylene
  • An example of integrated protective sheet 318, which has a backsheet function, according to the invention is as follows:
  • - protective sheet 312 comprising a first layer 319 of PET with a thickness of 50 ⁇ , such as MELINEX D243 by DUPONT, an interlayer of adhesive, for example ADCOTE A3305/CR857 of the DOW company, a second layer 320 of PET with a thickness of 250 ⁇ , such as MELINEX 238 by DUPONT, a further interlayer of adhesive, for example ADCOTE A3305/CR857 of the DOW company.
  • integrated protective sheet 418 acting as a frontsheet according to the invention is as follows:
  • an outer layer 419 of ETFE with a thickness of 50 ⁇ such as FLUOROSOL FT of the SAINT GOBAIN company
  • the invention has devised an encapsulating polymeric multilayer film which can be coupled to a protective film, frontsheet or backsheet, safely and durably.
  • the invention provides an encapsulating polymeric multilayer film which can be coupled to a protective sheet with known methods.
  • the invention provides an encapsulating polymeric multilayer film which is capable of improving the durability of a photovoltaic module to which it belongs, reducing the risks of delamination and of microbubbles.
  • the invention provides an encapsulating polymeric multilayer film which accordingly makes it possible to perfect a process for the production of photovoltaic modules which is simpler and cheaper than conventional ones.
  • the invention has devised an integrated protective backsheet or frontsheet of the integrated type which comprises an encapsulating film according to the same invention.
  • the invention provides an encapsulating polymeric multilayer film for cells of photovoltaic modules and an integrated protective backsheet or frontsheet comprising such film which can be manufactured with known systems and technologies.
  • the materials used may be any according to requirements and to the state of the art.

Abstract

An encapsulating polymeric multilayer film (10) for cells for photovoltaic modules, to be integrated by lamination with adhesive (1 1) with a protective sheet (12), backsheet or frontsheet, for photovoltaic cells of a photovoltaic module. The peculiarity of the multilayer film (10) resides in that it comprises - a first encapsulating polymeric layer (13), and - a second polymeric layer (14) for protecting the first encapsulating layer (13), intended for interaction with the layer of adhesive (1 1) interposed between the multilayer film (10) and the protective sheet (12).

Description

ENCAPSULATING POLYMERIC MULTILAYER FILM FOR CELLS FOR PHOTOVOLTAIC MODULES, AND PROTECTIVE INTEGRATED SHEET, OF THE TYPE OF A BACKSHEET OR FRONTSHEET, COMPRISING SUCH FILM
The present invention relates to an encapsulating polymeric multilayer film for cells for photovoltaic modules.
The present invention also relates to an integrated protective sheet, of the so-called backsheet or frontsheet type, which comprises a polymeric multilayer film according to the invention.
Generally, the typical structure of a first-generation photovoltaic module with crystalline silicon cells is constituted by the following main components: a glass sheet, a first upper encapsulating film, the photovoltaic cells interconnected by the electrical connection strips, a second lower encapsulating film, and a lower and generally laminated multilayer protective sheet, known in the jargon as backsheet.
In some cases, where low weight and flexibility are important, the glass sheet is replaced with a protective laminated sheet, known in the jargon as frontsheet.
In the case of second-generation photovoltaic modules with thin-film cells, the typical structure normally comprises the following layers: a glass sheet, the photovoltaic cell deposited as thin film on the glass, a lower encapsulating film, another glass sheet or a protective laminated sheet, i.e., the backsheet.
An alternative structure for the second-generation photovoltaic modules is the following: a frontsheet, i.e., a protective sheet made of ETFE (ethylene tetrafluoroethylene) or other protective transparent laminated element, an encapsulating film, arranged above, the photovoltaic cell deposited as thin film, on a lower sheet of metal or polymeric material.
Third-generation modules are currently also known but have only a limited diffusion; they have photoelectrochemical cells, for example Gratzel cells, or semiconducting polymers, for example cells with bulk heterojunctions, the typical structure of which is as follows: a protective upper encapsulating film which acts as a barrier against oxygen and humidity, a photovoltaic cell of the electrochemical type or with semiconducting polymers, a lower protective encapsulating film acting as a barrier against oxygen and humidity.
Currently, the production of a photovoltaic module consists in the manual or automated assembly of the various component layers and their discontinuous or continuous lamination with a process which typically provides for the application of heat and pressure.
Depending on the final quality of the product and on its durability over time, normally at least twenty years, the most critical operation in the production of a photovoltaic module is lamination.
The encapsulating film, in all of the above cited manufacturing solutions, with lamination is required to undergo deformation when hot in order to incorporate the cells, binding the upper and lower protective layers and thus forming the protective enclosure which, through the years, protects the electronics, i.e., the cells and the connections, against atmospheric attacks: humidity, solar radiation, particularly UV rays, hail, frost, pollutant atmospheric agents, etc.
These cited known photovoltaic module structures and the corresponding method of manufacture by lamination, despite being widespread, have drawbacks that entail the risk of causing quality defects.
The most important drawbacks are microbubbles, delamination and the presence of contaminants and impurities.
Humidity microbubbles are due to the condensation that is present on the surfaces of the components, in particular between the encapsulating film and the backsheet.
There are also trapped air microbubbles, caused by the air that can remain trapped between the various components of the module and in particular between the encapsulating film and the protective backsheet and/or frontsheet.
In general, microbubbles cause a series of functional problems as well as aesthetic ones, among which the most important are the reduction of the electrical insulation of the cell by accumulation of humidity therein and the reduction of the energy conversion efficiency of the photovoltaic module due to the reduced optical transmittance.
The delamination of the module between the encapsulating film and the protective backsheet or frontsheet is caused by the poor adhesion between the encapsulating film and the protective sheet.
This situation of poor adhesion can be ascribed to the migration and accumulation of humidity or other substances in the region of interface between the encapsulating film and the protective sheet and to the predominantly thermal stresses to which the photovoltaic module is subjected during its life.
As regards the presence of contaminants and impurities, the surface between the encapsulating film and the protective sheet, even if treated carefully, is normally contaminated by small impurities such as dust, organic deposits and others, caused by the production process.
Another drawback of the background art is due to the fact that the production process provides for the handling of each individual component of the module.
In particular, the module production line requires a machine that unwinds and cuts the encapsulating film and an adapted separate machine that unwinds and cuts the protective film. These machines affect significantly the cost of the product.
After the cutting operation, each component, including the encapsulating film and the protective backsheet or frontsheet, must be positioned precisely and carefully onto each other.
One currently known method for increasing the quality of the photovoltaic module while reducing production costs is to integrate the protective backsheet or frontsheet with the encapsulating film.
This can occur according to different methods.
A first method provides for simply resting the encapsulating film on the protective sheet, optionally with a gentle application of pressure and heat so as to provide a pre-laminated element which comprises these two layers.
A second method provides for coupling by lamination with adhesive. A third method provides for coupling by extrusion lamination.
A fourth method provides for the spreading of the encapsulating film on the protective sheet (extrusion coating).
Although these methods are widespread, each one has in any case at least some of the problems cited above.
In particular, the method by simple resting contact does not solve the problem of microbubbles or the drawback of the risk of delamination.
The method of coupling by lamination with adhesive entails limitations and risks linked to the possible interactions among components of the encapsulating film and particularly the peroxides and silanes, with the components of the adhesive, in particular in relation to the durability of the photovoltaic module.
The method of coupling by extrusion lamination does not solve the problem of limited adhesion, i.e., of delamination risks.
The method of coating the encapsulating film on the protective film also has the problem of limited adhesion with risk of delamination.
Moreover, lamination between the encapsulating film, which is extremely elastic, and the protective sheet, which is typically rigid or semirigid, can entail defects such as creases, wrinkles and small air bubbles which remain trapped in the lamination.
A standard encapsulating film is usually based on EVA, and peroxides and silanes must be present in its formulation. The peroxides are necessary because the film of EVA as such, being a thermoplastic material with a low melting point (approximately 60-70°C), cannot withstand the operating temperatures (where sometimes the photovoltaic modules reach temperatures of even 60-70°C and in any case are typically tested up to 85°C).
The peroxides, during the lamination of the module (hot, typically at the temperature of approximately 150°C for a time of approximately 15 min) break down, trigger the cross-linking of the EVA polymer and trigger the linking of the silane molecules to the molecular chain of the EVA polymer.
The need to use an EVA film with a low melting point is linked to the needs to have very high transparency, which means having no losses of conversion efficiency of the module, which cannot be achieved by using an EVA film with a high melting point, i.e., with higher crystallinity.
Silanes are instead necessary to improve the adhesion of the encapsulating EVA film to the glass and in general to polar surfaces (such as those of the cells and of the electrical contacts).
The silanes react with the polar surfaces, developing a very strong chemical bond which is stable even in the presence of humidity.
Since EVA is a polar material with a certain affinity for water, water can accumulate and permeate the EVA, reaching over time the surface between the glass and the encapsulating element. Here it becomes interposed between the EVA and the glass, reducing mutual adhesion drastically.
Thanks to the silanes, the EVA film maintains its adhesion with respect to the cited surfaces even in the presence of humidity which, due to prolonged exposure to bad weather, can always accumulate within the photovoltaic module.
Peroxides are highly aggressive substances which have a low molecular weight and therefore migrate easily in the encapsulating film. Peroxides can therefore migrate over time until they reach the layer of adhesive that indeed binds the encapsulating film to the protective frontsheet or backsheet.
If this occurs, the peroxides attack and degrade the adhesive, whose performance is reduced drastically.
If this occurs, the photovoltaic module, which is always exposed to the inclemency of the weather, delaminates in the region between the encapsulating element and the backsheet and/or frontsheet, thus inducing regions of accumulation of humidity and air, and this leads to partial or total damage to the module, with loss of electrical insulation, loss of conversion efficiency, et cetera.
The silanes, too, can likewise reduce partly the performance of the adhesive, since after migration they can react with the adhesive and can reduce its ability to cross-link and bind to the surfaces of the encapsulating element from one side of the frontsheet and/or backsheet from the other.
The aim of the present invention is to provide an encapsulating polymeric multilayer film for cells of photovoltaic modules which makes it possible to encapsulate a photovoltaic cell without the drawbacks cited above.
Within the scope of this aim, an object of the invention is to provide an encapsulating polymeric multilayer film that can be coupled to a protective frontsheet or backsheet film safely and durably.
Another object of the invention is to provide an encapsulating polymeric multilayer film which can be coupled to a protective sheet with methods of a known type.
A further object of the invention is to provide an encapsulating polymeric multilayer film which is capable of improving the durability of a photovoltaic module to which it belongs by reducing the risks of delamination and of microbubbles.
Another object of the invention is to provide an encapsulating polymeric multilayer film that accordingly makes it possible to devise a process for the production of photovoltaic modules which is simpler and cheaper than known ones.
Another object of the invention is to devise an integrated protective backsheet or frontsheet of the integrated type, which comprises an encapsulating film according to the same invention.
Another object of the invention is to propose an encapsulating polymeric multilayer film for cells of photovoltaic modules and an integrated protective backsheet or frontsheet comprising said film which can be manufactured with known systems and technologies.
This aim, as well as these and other objects which will become better apparent hereinafter, are achieved by an encapsulating polymeric multilayer film for cells for photovoltaic modules, to be integrated by lamination with adhesive with a protective sheet, backsheet or frontsheet, for photovoltaic cells of a photovoltaic module, characterized in that it comprises
- a first encapsulating polymeric layer, and
- a second polymeric layer for protecting said first encapsulating layer, intended for interaction with the layer of adhesive interposed between said multilayer film and the protective film.
Further characteristics and advantages of the invention will become better apparent from the description of three preferred but not exclusive embodiments of the encapsulating polymeric multilayer film according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:
Figure 1 is a schematic sectional view of a multilayer film according to the invention in a first embodiment thereof;
Figure 2 is a schematic sectional view of a multilayer film according to the invention in a second embodiment thereof;
Figure 3 is a schematic sectional view of a multilayer film according to the invention in a third embodiment thereof; Figure 4 is a schematic sectional view of an integrated protective sheet according to the invention;
Figure 5 is a schematic sectional view of a second embodiment of an integrated protective sheet according to the invention.
With reference to the figures, an encapsulating polymeric multilayer film for cells for photovoltaic modules according to the invention is generally designated by the reference numeral 10.
The multilayer film 10 is intended to be integrated by lamination with adhesive 1 1 with a protective backsheet or frontsheet 12 for the photovoltaic cells of a photovoltaic module.
The multilayer film 10 comprises:
- a first encapsulating polymeric layer 13, and
- a second polymeric layer 14 for protecting the first encapsulating layer 13, intended for interaction with the layer of adhesive 1 1 interposed between the multilayer film 10 and the protective sheet 12.
The second layer 14 has no additives that can compromise adhesion and its durability and in particular is free from residual peroxides, non- linked silanes, slip agents, and the like.
The second layer 14 also acts as a barrier against the migration of these substances, i.e., silanes and peroxides, from the first layer 13 toward the adhesive layer 1 1 , and also acts as a barrier against the passage of any residues of solvent or of not cross-linked adhesive from the adhesive layer 1 1 toward the first layer 13.
The second layer 14 is composed of a polymer with high resistance to deformation when heated (creep) and to the migration of peroxides and silanes.
Creep resistance is important because the photovoltaic module, in the conditions for use and testing, is subjected to high temperatures, as indicated above, and at these temperatures it is necessary to ensure that the cells cannot move, overlap or tension the electrical connections or even detach from them.
In particular, the second layer 14 comprises a semicrystalline thermoplastic polymer whose melting point is higher than 85°C and preferably higher than 95°C.
A semicrystalline thermoplastic polymer with these characteristics achieves the aim of contrasting the migration of silanes and peroxides from the first layer 13, through the second layer 14, toward the adhesive layer 1 1.
As the crystallinity of the thermoplastic polymer increases, it opposes increasingly the migration of permeating agents, i.e., silanes and peroxides, which on the contrary diffuse well in the amorphous phase and very poorly in the crystalline phase.
Since each crystalline phase is characterized by a typical melting point, and since in general the higher the crystalline phase and the higher the melting point of the material (as detected by the melting peak of the classical calorimetric differential thermal analysis (DSC)), in order to limit and if possible prevent permeation it is necessary to use semicrystalline polymers with the highest possible melting point, certainly higher than the operating conditions. One does not venture in any case beyond certain temperature limits, since excessively crystalline polymers tend to behave mechanically in a fragile manner and therefore the photovoltaic module that incorporates them, subjected in operation and during testing to temperatures even below zero (-40°C), can reveal cracks, delaminations, separations, et cetera.
The semicrystalline thermoplastic polymer is present in the second layer 14 in a percentage between 40% and 100%, preferably between 60% and 100%, and in particular 100%.
If the semicrystalline thermoplastic polymer is not present in the percentage of 100%, the remaining percentage is to be understood as being constituted by other thermoplastic polymers.
The second layer 14 has a thickness comprised between 1 and 400 μηι, preferably between 50 and 150 μηι, and in particular between 75 and 125 μηι.
Advantageously, the semicrystalline thermoplastic polymer present in the second layer 14 is constituted by a polymer chosen among: low-density polyethylene (LDPE), low-density linear polyethylene (LLDPE), high- density polyethylene (HDPE), and other similar and equivalent materials, or, as an alternative, by polar copolymers of ethylene, such as ethyl vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethyl butyl acrylate (EBA), and other similar and equivalent materials.
In particular, and preferably, the semicrystalline thermoplastic polymer present in the second layer 14 is constituted by EVA with a vinyl acetate content of less than 20%, preferably less than 10% and in particular less than 6%, with a melt flow rate of less than 50 g/10 min, preferably less than 20 g/10 min and in particular less than 5 g/10 min, the melt flow index being understood as measured at 190 °C and with 2.16 kg of thrust.
The cited semicrystalline thermoplastic polymers with these characteristics have a substantially apolar chemical structure (LDPE, LLDPE, HDPE) or a weakly polar one (EVA) and since the potential migrating substances are all polar, this further limits their migration.
The second layer 14 can receive the addition of mineral fillers, such as calcium carbonate, talc, aluminum trihydroxide, titanium dioxide and the like, or organic fillers, such as carbon black, which are adapted to give high resistance to creep.
Since the second layer 14 has no peroxides, it must nonetheless be able to provide high resistance to creep.
The mineral fillers are preferably comprised in a percentage between 1% and 60%, and particularly between 10% and 40%.
The outer face of the second layer 14 is preset for lamination operations by means of per se known pretreatment techniques, such as corona treatment, flame treatment, plasma treatment, priming and the like. The second layer 14 can have UV and thermal stabilizing additives, such as for example UV stabilizers of the family of sterically hindered amines (HALS), such as for example TINUVIN® 770 of the BASF company, UV absorbers (UVA) of the benzophenone family, for example CYASORB® UV-531 by the Cytech company, or benzotriazoles, for example TINUVIN® 326 of the BASF company, or thermal stabilizers, such as for example IRGAFOS® 168 of the BASF company.
The second layer 14 also acts as a barrier against humidity, thanks to a water vapor permeability (WVTR) of less than 25 g/m2 per day, preferably less than 5 g/m2 per day, measured at 23°C and 85/15 RH.
The second layer 14 has stiffness properties adapted to facilitate the workability of the film 10, by means of a traction elasticity modulus (Young's modulus) of more than 50 MPa and preferably more than 100 MPa.
In a constructive variation of the multilayer film 10 according to the invention, the second layer 14 comprises an amorphous thermoplastic polymer, not a semicrystalline one, whose glass transition temperature is higher than 85°C and preferably higher than 105°C.
A similar second layer 14 is composed of a polymer with additives adapted to cross-link by heat or humidity or another technique such as irradiation with gamma rays and the like, prior to lamination of the photovoltaic module.
These additives are constituted by
- peroxides with a characteristic breakdown temperature that is lower than the characteristic breakdown temperature of the peroxides contained in the first layer 13 and adapted to allow the first layer 13 to cross-link by application of heat prior to lamination;
- silane compounds adapted to link, by means of peroxides, during an operation of extrusion of the second layer 14, to the molecular chains of the polymer of the second layer, or already linked to the molecular chain of the polymer of the second layer 14, adapted to allow the cross-linking of the layer 13 due to humidity and optionally also to the heat prior to the production of the photovoltaic module for which the film 10 is intended.
The peroxides and silanes, despite being present, are not "free" to migrate, but are already linked and no longer dangerous once the film 10 has been coupled to the adhesive layer 1 1.
The multilayer film 10 can comprise pigments and colors adapted to give the desired color of the integrated backsheet that incorporates it.
The first layer 13 is composed of a thermoplastic polymer that contains cross-linking agents.
The thermoplastic polymer that defines the first layer 13 is EVA, for example of the type of Elvax 150W by the Dupont company.
The first layer 13 receives the addition of cross-linking agents such as peroxides, binding agents such as silanes, and UV and thermal stabilizing additives.
The peroxides are organic peroxides, for example of the peroxycarbonate family, for example LUPEROX TBEX of the ARKEMA company.
The bonding agents are for example organic silanes, for example of the family of methacryloxypropyltrimethoxysilanes (MTMSI), for example Z-6030 of the Dow Corning company.
The UV stabilizing agents are constituted by sterically hindered amines (HALS), for example TINUVIN® 770 by the BASF company, UV absorbers (UVA) of the benzophenone family, such as CYASORB UV-531 of the CYTECH company, or benzotriazoles such as TINUVIN® 326 of the BASF company, and thermal stabilizers such as IRGAFOS® 168 of the BASF company.
The thickness of the first layer 13 is comprised between 50 and 1000 μιτι and is preferably comprised between 250 and 500 μιη.
The first layer 13 can be constituted by a mixture of predominantly amorphous thermoplastic polymer as described above and other thermoplastic polymers. Preferably, the predominantly amorphous thermoplastic polymer is present in a percentage between 40% and 100%, more preferably is present in a percentage between 60% and 100%, and in particular is present as 100%.
In another variation of execution thereof, the first layer 13 is based on a thermoplastic polymer without cross-linking agents, such as for example ethylene methacrylate (EMA).
In a further variation of execution thereof, the first layer 13 comprises low-density linear polyethylene (LLPDE) and additives such as silanes which are adapted to cross-link due to humidity or other known method during the lamination of the photovoltaic module.
In a second embodiment, which also exemplifies and does not constrain the invention, illustrated in Figure 2, the encapsulating polymeric multilayer film 1 10 comprises a third layer 1 15, which acts as a binder and is intermediate between the first layer 1 13 and the second layer 1 14, with the second layer 1 14 in contact with the adhesive 1 1 1 , for connection to a generic protective sheet 1 12.
The third layer 1 15 is composed of a mixture of polymers which are present in the first layer 1 13 and in the second layer 1 14.
As an alternative, the third layer 1 15 is constituted by binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA) and the like, or by a mixture of the polymers that are present in the first layer 113 and in the second layer 1 14 with the binding polymers.
In a third embodiment of the invention, which also is to be understood as exemplifying and not limiting it, shown schematically in Figure 3, the encapsulating polymeric multilayer film 210 comprises a third intermediate barrier layer 215, which is joined to the first layer 213 by means of a fourth layer 216 which acts as a binder, and is joined to the second layer 214 by means of a fifth layer 217 which acts as a binder.
The third layer 215 is constituted for example by an oxygen barrier polymer, such as ethylene vinyl alcohol (EVOH), polyamide (PA), and the like, while the fourth layer 216 and the fifth layer 217 are made of binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA), and the like.
The adhesive layer 1 1 , 1 1 1, 21 1 is of a type chosen among polyurethane adhesives, polyester adhesives, epoxy adhesives, and the like, and for example is constituted by a two-part solvent-based polyurethane adhesive.
As regards production, the film 10 according to the invention is characterized in that the first and second layers are coupled by means of a coextrusion process.
As an alternative, the first and second layers are coupled by means of a process of extrusion coating of the first layer on the second layer.
According to a further alternative, the first and second layers are coupled by means of a simple resting contact process.
According to yet another alternative, the first and second layers can be coupled by means of a process of lamination with extrusion.
The film 10 can be supplied to the coupling with the protective sheet 12 in turn with a protective sheet or liner, to avoid transfer into the reel of peroxides and silanes, for example a sheet of high-density polyethylene (HDPE).
The present invention also relates to a protective sheet, designated in
Figure 4 by the reference numeral 318, of the backsheet or frontsheet type, which is integrated with an encapsulating polymeric layer, for the protection of cells of photovoltaic modules.
The peculiarity of such an integrated protective sheet 318 is that it comprises - a mono- or multilayer protective sheet 312,
- an intermediate layer of adhesive 311 for joining with an encapsulating polymeric multilayer film 310 according to one or more of its embodiments and variations described above.
The integrated protective sheet 318 has a protective film 312 which comprises a first layer of PET (polyethylene terephthalate) 319, which is external, and a second layer of PET 320, which is internal, interlaid by a layer of adhesive 321 , and is intended to be used as a backsheet.
The background art instead normally provides for a protective backsheet to comprise three layers, for example a first layer of PET, a second layer of PET, and a third binding layer where the coupling layer can be EVA, PA, an ionomer, and the like.
A further example of three-layer backsheet comprises a first layer of PVF (known as "Tedlar", by the DuPont company, which is mostly used), a second layer of PET, and a third layer again made of PVF.
The cited layers of the two examples of backsheet are typically coupled by means of adhesive (polyester-based, polyurethane based, but not only).
The integrated protective sheet 318, of the backsheet type, therefore has a protective sheet 312 which lacks the third sealing layer and only has the two layers 319 and 320 made of PET.
This solution frees a backsheet manufacturer from the need to manufacture products with a sealing layer that must be different for each different class of encapsulating layer, since joining occurs by means of an adhesive layer 311 as described above and the adhesive layer 31 1 is protected by the second layer 14 of the encapsulating multilayer film 10, 1 10 and 210 according to the invention as described above.
Moreover, the integrated protective sheet 318 offers better quality, understood as defect reduction, since with the second layer 14 that acts also as an agent for coupling to the encapsulating layer there is one less surface and therefore a smaller risk of condensation and various contaminations.
In a different embodiment thereof, to be used as a frontsheet, the integrated protective sheet 418 according to the invention has a protective film 412 which comprises an outer layer 419 made of EFTE (ethylene tetrafluoroethylene) and a layer of adhesive 420.
An example of integrated protective sheet 318, which has a backsheet function, according to the invention is as follows:
- protective sheet 312, comprising a first layer 319 of PET with a thickness of 50 μιη, such as MELINEX D243 by DUPONT, an interlayer of adhesive, for example ADCOTE A3305/CR857 of the DOW company, a second layer 320 of PET with a thickness of 250 μιη, such as MELINEX 238 by DUPONT, a further interlayer of adhesive, for example ADCOTE A3305/CR857 of the DOW company.
- an encapsulating polymeric multilayer film 10, 1 10, 210 as described above.
An example of integrated protective sheet 418 acting as a frontsheet according to the invention is as follows:
- an outer layer 419 of ETFE with a thickness of 50 μπι, such as FLUOROSOL FT of the SAINT GOBAIN company,
- a layer of two-part solvent-based polyester-based adhesive such as
DOW ADCOTE A3307/CR 857,
- an encapsulating polymeric multilayer film 10, 1 10 and 210 according to what has been described above.
In practice it has been found that the invention achieves the intended aim and objects.
In particular, the invention has devised an encapsulating polymeric multilayer film which can be coupled to a protective film, frontsheet or backsheet, safely and durably.
Moreover, the invention provides an encapsulating polymeric multilayer film which can be coupled to a protective sheet with known methods.
Furthermore, the invention provides an encapsulating polymeric multilayer film which is capable of improving the durability of a photovoltaic module to which it belongs, reducing the risks of delamination and of microbubbles.
Moreover, the invention provides an encapsulating polymeric multilayer film which accordingly makes it possible to perfect a process for the production of photovoltaic modules which is simpler and cheaper than conventional ones.
Moreover, the invention has devised an integrated protective backsheet or frontsheet of the integrated type which comprises an encapsulating film according to the same invention.
Not least, the invention provides an encapsulating polymeric multilayer film for cells of photovoltaic modules and an integrated protective backsheet or frontsheet comprising such film which can be manufactured with known systems and technologies.
The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. All the details may furthermore be replaced with other technically equivalent elements.
In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent dimensions, may be any according to requirements and to the state of the art.
The disclosures in Italian Patent Application no. PD201 1A0001 16, from which this application claims priority, are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. An encapsulating polymeric multilayer film (10) for cells for photovoltaic modules, to be integrated by lamination with adhesive (1 1) with a protective sheet (12), backsheet or frontsheet, for photovoltaic cells of a photovoltaic module, characterized in that it comprises
- a first encapsulating polymeric layer (13), and
- a second polymeric layer (14) for protecting said first encapsulating layer (13), intended for interaction with the layer of adhesive (1 1) interposed between said multilayer film (10) and the protective sheet (12).
2. The multilayer film according to claim 1 , characterized in that said second layer (14) acts as a barrier against the migration of said substances from said first layer (13) toward said adhesive layer (1 1) and acts as a barrier against the passage of any residues of solvent or not completely cross-linked adhesive from said adhesive layer (1 1) toward said first layer (13).
3. The multilayer film according to the preceding claims, characterized in that said second layer (14) is composed of a polymer with high resistance to deformation when heated (creep) and to the migration of peroxides and silanes.
4. The multilayer film according to the preceding claims, characterized in that said second layer (14) comprises a semicrystalline thermoplastic polymer whose melting point is higher than 85 °C and preferably higher than 95°C.
5. The multilayer film according to the preceding claim, characterized in that said semicrystalline thermoplastic polymer is present in said second layer (14) in a percentage between 40% and 100%, preferably between 60% and 100%, and in particular 100%.
6. The multilayer film according to the preceding claims, characterized in that said second layer (14) has a thickness comprised between 1 and 400 μπι, preferably between 50 and 150 μηι, and in particular between 75 and 125 μηι.
7. The multilayer film according to the preceding claims, characterized in that said semicrystalline thermoplastic polymer present in said second layer (14) is constituted by a polymer chosen among: low- density polyethylene (LDPE), low-density linear polyethylene (LLDPE), high-density polyethylene (HDPE), and other similar and equivalent materials, or, as an alternative, by polar copolymers of ethylene, such as ethyl vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethyl butyl acrylate (EBA), and other similar and equivalent materials.
8. The multilayer film according to the preceding claim, characterized in that said semicrystalline thermoplastic polymer present in said second layer (14) is constituted by EVA with a vinyl acetate content of less than 20%, preferably less than 10% and in particular less than 6%, with a melt flow rate of less than 50 g/10 min, preferably less than 20 g/10 min and in particular less than 5 g/10 min, said melt flow index being measured at 190 °C and with 2.16 kg of thrust.
9. The multilayer film according to the preceding claims, characterized in that said second layer (14) receives the addition of mineral fillers, such as calcium carbonate, talc, aluminum trihydroxide, titanium dioxide and the like, or organic fillers, such as carbon black, which are adapted to give high resistance to creep.
10. The multilayer film according to the preceding claims, characterized in that the outer face of said second layer (14) is preset for lamination operations by means of pretreatment techniques, such as corona treatment, flame treatment, plasma treatment, priming and the like.
1 1. The multilayer film according to the preceding claims, characterized in that said second layer (14) has UV and thermal stabilizing additives, such as for example UV stabilizers of the family of sterically hindered amines (HALS) such as for example TINUVIN® 770 of the BASF company, UV absorbers (UVA) of the benzophenone family, for example CYASORB® UV-531 by the Cytech company, or benzotriazoles, for example TINUVIN® 326 of the BASF company, or thermal stabilizers, such as for example IRGAFOS® 168 of the BASF company.
12. The multilayer film according to the preceding claims, characterized in that said second layer (14) acts as a barrier against humidity, thanks to a water vapor permeability (WVTR) of less than 25 g/m2 per day, preferably less than 5 g/m2 per day, measured at 23°C and 85/15 RH.
13. The multilayer film according to the preceding claims, characterized in that said second layer (14) has stiffness properties adapted to facilitate the workability of the film, thanks to a traction elasticity modulus (Young's modulus) of more than 50 MPa and preferably more than 100 MPa.
14. The multilayer film according to claims 1 to 3 and 6 to 13, characterized in that said second layer (14) comprises an amorphous thermoplastic polymer whose glass transition temperature is higher than 85°C and preferably higher than 105°C.
15. The multilayer film according to claims 1 to 3 and 6 to 13, characterized in that said second layer (14) is composed of a polymer with additives adapted to cross-link by heat or humidity or another technique such as irradiation with gamma rays and the like, prior to lamination of the photovoltaic module.
16. The multilayer film according to the preceding claim, characterized in that said additives are constituted by
- peroxides with a characteristic breakdown temperature that is lower than the characteristic breakdown temperature of the peroxides contained in the first layer (13) and adapted to allow the layer (13) to cross-link by application of heat prior to lamination;
- silane compounds adapted to link, by means of peroxides, during an operation of extrusion of the second layer (14), to the molecular chains of the polymer of said second layer, or already linked to the molecular chain of said polymer of the second layer (14), adapted to allow the cross-linking of the layer (13) due to humidity and optionally also to the heat prior to the production of the photovoltaic module for which the film (10) is intended.
17. The multilayer film according to the preceding claims, characterized in that it comprises pigments and colors adapted to give the desired color of the integrated backsheet.
18. The multilayer film according to one or more of the preceding claims, characterized in that said first layer (13) is composed of a thermoplastic polymer that contains cross-linking agents.
19. The multilayer film according to the preceding claim, characterized in that said thermoplastic polymer is EVA, for example of the type of Elvax 150W by the Dupont company.
20. The multilayer film according to the preceding claims, characterized in that said first layer (13) receives the addition of cross- linking agents such as peroxides, binding agents such as silanes, and UV and thermal stabilizing additives.
21. The multilayer film according to claims 19 and 20, characterized in that the thickness of the first layer (13) is comprised between 50 and 1000 μιη and is preferably comprised between 250 and 500 μηι.
22. The multilayer film according to claims 1 to 17, characterized in that said first layer (13) is based on a thermoplastic polymer without cross- linking agents, such as for example ethylene methylacrylate (EMA).
23. The multilayer film according to claims 1 to 17, characterized in that said first layer (13) comprises low-density linear polyethylene (LLPDE) and additives, such as silanes, which are adapted to cross-link due to the effect of humidity or other known method during the lamination of the photovoltaic module.
24. An encapsulating polymeric multilayer film according to one or more of the preceding claims, characterized in that it comprises a third layer (1 15), which acts as a binder and is intermediate between said first layer
(1 13) and said second layer (1 14).
25. The polymeric multilayer film according to the preceding claim, characterized in that said third layer (1 15) is composed of a mixture of polymers which are present in the first layer (1 13) and in the second layer
(1 14) .
26. The polymeric multilayer film according to claim 24, characterized in that said third layer (1 15) is constituted by binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA) and the like, or by a mixture of the polymers that are present in the first and second layers with said binding polymers.
27. The encapsulating polymeric multilayer film according to one or more of the preceding claims, characterized in that it comprises a third intermediate barrier layer (215), which is joined to said first layer (213) by means of a fourth layer (216) which acts as a binder, and is joined to said second layer (214) by means of a fifth layer (217) which acts as a binder.
28. The polymeric multilayer film according to the preceding claim, characterized in that said third layer (215) is constituted by an oxygen barrier polymer, such as ethylene vinyl alcohol (EVOH), polyamide (PA), and the like, said fourth layer (216) and said fifth layer (217) being made of binding polymers, such as for example copolymers of EVA linked with maleic anhydride (MAH), copolymers of EVA linked with glycidyl methacrylate (GMA), and the like.
29. The film according to the preceding claims, characterized in that said adhesive layer (1 1 , 1 1 1 , 21 1) is of a type chosen among polyurethane adhesives, polyester adhesives, epoxy adhesives, and the like, and for example is constituted by a two-part solvent-based polyurethane adhesive.
30. The film according to one or more of the preceding claims, characterized in that said first and second layers are coupled by means of a coextrusion process.
31. The film according to one or more of claims 1 to 29, characterized in that said first and second layers are coupled by means of a process of extrusion coating of the first layer on the second layer.
32. The film according to one or more of claims 1 to 29, characterized in that said first and second layers are coupled by means of a simple resting contact process.
33. The film according to the preceding claims, characterized in that said first and second layers can be coupled by means of a process of lamination with extrusion.
34. The film according to one or more of the preceding claims, characterized in that it is protected by a protective sheet or liner to avoid transfer into the reel of peroxides and silanes, for example a sheet of high- density polyethylene (HDPE).
35. A protective sheet (318), of the type of a backsheet or frontsheet, integrated with an encapsulating polymeric layer, for the protection of cells of photovoltaic modules, characterized in that it comprises
- a mono- or multilayer protective sheet (312)
- an intermediate layer of adhesive (31 1) for joining with an encapsulating polymeric multilayer film (10, 1 10, 210) according to one or more of claims 1 to 34.
36. The integrated protective sheet according to claim 35, characterized in that said protective sheet (312) comprises a first layer of PET (319), which is external, and a second layer of PET (320), which is internal, interlaid by a layer of adhesive (321), and is intended to be used as a backsheet.
37. The integrated protective sheet according to claim 35, characterized in that said protective sheet (412) comprises an outer layer (419) made of EFTE and a layer of adhesive (420) and is intended to be used as a frontsheet.
PCT/IB2012/051781 2011-04-13 2012-04-12 Encapsulating polymeric multilayer film for cells for photovoltaic modules, and protective integrated sheet, of the type of a backsheet or frontsheet, comprising such film WO2012140585A1 (en)

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ITPD2011A000116 2011-04-13
IT000116A ITPD20110116A1 (en) 2011-04-13 2011-04-13 MULTI-LAYER POLYMER FILM INSULATED FOR CELLS FOR PHOTOVOLTAIC MODULES, AND INTEGRATED PROTECTIVE SHEET, TYPE 'BACKSHEET' OR 'FRONTSHEET' INCLUDING SUCH FILM

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