WO2020109968A1 - Adhesive composition, light redirecting film and solar cell module - Google Patents

Adhesive composition, light redirecting film and solar cell module Download PDF

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Publication number
WO2020109968A1
WO2020109968A1 PCT/IB2019/060126 IB2019060126W WO2020109968A1 WO 2020109968 A1 WO2020109968 A1 WO 2020109968A1 IB 2019060126 W IB2019060126 W IB 2019060126W WO 2020109968 A1 WO2020109968 A1 WO 2020109968A1
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WIPO (PCT)
Prior art keywords
adhesive composition
light redirecting
redirecting film
layer
composition according
Prior art date
Application number
PCT/IB2019/060126
Other languages
French (fr)
Inventor
Yiwen Chu
Yuting WAN
Rui PAN
Original Assignee
3M Innovative Properties Company
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Publication date
Application filed by 3M Innovative Properties Company filed Critical 3M Innovative Properties Company
Publication of WO2020109968A1 publication Critical patent/WO2020109968A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/06—Non-macromolecular additives organic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J123/00—Adhesives based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Adhesives based on derivatives of such polymers
    • C09J123/02—Adhesives based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Adhesives based on derivatives of such polymers not modified by chemical after-treatment
    • C09J123/04—Homopolymers or copolymers of ethene
    • C09J123/08—Copolymers of ethene
    • C09J123/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
    • C09J123/0815—Copolymers of ethene with aliphatic 1-olefins
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J123/00—Adhesives based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Adhesives based on derivatives of such polymers
    • C09J123/02—Adhesives based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Adhesives based on derivatives of such polymers not modified by chemical after-treatment
    • C09J123/04—Homopolymers or copolymers of ethene
    • C09J123/08—Copolymers of ethene
    • C09J123/0846—Copolymers of ethene with unsaturated hydrocarbons containing other atoms than carbon or hydrogen atoms
    • C09J123/0853—Vinylacetate
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0053—Prismatic sheet or layer; Brightness enhancement element, sheet or layer
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0055—Reflecting element, sheet or layer
    • 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
    • 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
    • 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
    • H01L31/05—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • 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
    • H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
    • 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
    • H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
    • H01L31/0547—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means comprising light concentrating means of the reflecting type, e.g. parabolic mirrors, concentrators using total internal reflection
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2203/00—Applications of adhesives in processes or use of adhesives in the form of films or foils
    • C09J2203/322—Applications of adhesives in processes or use of adhesives in the form of films or foils for the production of solar panels
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2423/00—Presence of polyolefin
    • 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
    • Y02E10/52—PV systems with concentrators

Definitions

  • the invention relates to the technical field of photovoltaic cells, in particular to an adhesive composition, and a light redirecting film and a solar cell module comprising the same.
  • a solar cell is a device that uses solar energy to generate electricity.
  • the common solar cells include a battery body that is encapsulated in an encapsulation cover and an encapsulation back sheet. Light is incident on the light-facing surface of the battery body through the encapsulation cover, and the battery body converts the light energy in the light into electrical energy.
  • a light redirecting film may be provided inside the solar cell module. When power is generated by the solar cell module, a light may be irradiated onto an optical structure of the light redirecting film after passing through a light transmissive element. The optical structure of the light redirecting film can reflect the incident light and change the direction thereof. Since the light is incident from top to bottom, the light redirecting film reflects the light upward toward the light transmissive element.
  • the light redirecting film is usually disposed on the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module by an adhesive layer.
  • the adhesive layer gradually ages over time, and bulges are generated between the light redirecting film and the package back sheet, thereby causing the light redirecting film to be broken or fall off from the adhering surface.
  • an object of the present invention is to provide an adhesive material having good moisture-heat aging resistance for a solar cell module, which has high adhesion and does not produce bulges in the adhesive layer under a moisture-heat aging condition.
  • an adhesive composition comprising a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction at a temperature of 95°C or more and has an exothermic amount of 2-40 J/g.
  • the resin base material is one or more selected from a group consisting of an ethylene-vinyl acetate (EVA) copolymer, a polyolefin (PO) resin, polypropylene oxide (PP), polyvinyl butyral (PVB), a
  • EVA ethylene-vinyl acetate
  • PO polyolefin
  • PP polypropylene oxide
  • PVB polyvinyl butyral
  • TSV tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer
  • ETFE ethyl ene-tetrafluoroethylene copolymer
  • PVDF polyvinylidene fluoride
  • PU polyurethane
  • PMMA polymethylmethacrylate
  • PI polyimide
  • the resin base material has a melt flow index (MFI) in a range of 10-30.
  • the resin base material is an ethylene-vinyl acetate (EVA) copolymer.
  • a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 24-30 wt%.
  • a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 26-28 wt%.
  • the peroxide crosslinking agent is one or more selected from a group consisting of benzoyl peroxide (BPO), dicumyl peroxide (DCP), t-amyl peroxyacetate (TAP A), tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH).
  • BPO benzoyl peroxide
  • DCP dicumyl peroxide
  • TAP A t-amyl peroxyacetate
  • TBEC tert-butyl peroxy-2-ethylhexyl carbonate
  • TBPMH tert-butyl peroxy-3, 5, 5-trimethyl hexanoate
  • the non-peroxide crosslinking agent is one or more selected from a group consisting of trimethylolpropane triacrylate (TMPTA) and triallyl isocyanurate (TAIC).
  • TMPTA trimethylolpropane triacrylate
  • TAIC triallyl isocyanurate
  • the coupling agent is one or more selected from a group consisting of a silane coupling agent and a phthalic ester coupling agent.
  • the ultraviolet absorber is one or more selected from a group consisting of a salicyl ester ultraviolet absorber, a
  • benzophenone ultraviolet absorber a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber.
  • the salicyl ester ultraviolet absorber is one or more selected from a group consisting of methyl salicylate, ethyl salicylate and octyl salicylate.
  • the benzophenone ultraviolet absorber is one or more selected from a group consisting of
  • the benzotriazole ultraviolet absorber is one or more selected from a group consisting of
  • the ultraviolet stabilizer is a hindered amine ultraviolet stabilizer.
  • the hindered amine ultraviolet stabilizer is one or more selected from a group consisting of polysuccinic acid
  • a light redirecting film comprising a light redirecting layer, a base layer and a reactive adhesive layer in turn, wherein the reactive adhesive layer comprises the above adhesive composition.
  • the base layer has been subjected to a physical surface treatment.
  • the physical surface treatment is corona treatment or plasma treatment.
  • the reactive adhesive layer has a thickness in a range of 10-100 pm.
  • the light redirecting layer comprises a plurality of microstructures that are orderly arranged and protruded from the base layer.
  • the light redirecting layer comprises a plurality of microstructures that are randomly arranged and protruded from the base layer.
  • the plurality of microstructures comprises an array of abutting triangular prisms whose orientation direction is non-linearly oriented.
  • the plurality of microstructures comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane.
  • the light redirecting film further comprises a primer layer between the reactive adhesive layer and the base layer.
  • the primer layer is a polyester primer layer or a polyacrylate primer layer.
  • the light redirecting film further comprises a light reflecting layer, wherein the light reflecting layer covers the plurality of microstructures and conforms to the plurality of microstructures.
  • a solar cell module comprising a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet sequentially disposed along a thickness direction of the solar cell module, wherein the solar cell module further includes the above light redirecting film, which is provided between the post encapsulation layer and the back sheet and adheres to a surface of the back sheet through the reactive adhesive layer.
  • a side of the back sheet facing the solar cells comprises a non-hot melt adhesive material.
  • a side of the back sheet facing the solar cells comprises a fluorine-containing material.
  • the adhesive layer has high adhesion
  • the relative positional drift of the light redirecting film during the high temperature laminating process for the solar cell module may be greatly reduced.
  • Fig. 1 shows a cross-sectional view of a light redirecting film according to an embodiment of the invention
  • Fig. 2 shows a perspective view of an array of parallel triangular prisms included in a light redirecting film according to an embodiment of the invention
  • Fig. 3 shows a cross-sectional view of a solar cell module according to an embodiment of the invention.
  • a light redirecting film is usually disposed on the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module by an adhesive layer.
  • the adhesive layer gradually ages over time, and bulges are generated between the light redirecting film and the package back sheet, thereby causing the light redirecting film to be broken or fall off from the adhering surface.
  • an adhesive composition comprising a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction in a lamination process for producing a solar cell module (generally, a lamination temperature of 140°C or higher) and has an exothermic amount of 2-40 J/g.
  • the reason for the formation of bulges that can be discerned by naked eyes between the light redirecting film and the back sheet during the moisture-heat aging of the adhesive layer is as follows. Under aging conditions (for example, 85°C / 85% humidity), the resin in the adhesive layer softens and melts, resulting in a decrease in adhesion to the light redirecting film and the back sheet. At the same time, the water vapor in the environment and small molecular gases in the module will accumulate at a position having a weak bonding force to form bulges.
  • the bulges may be formed anywhere within the light redirecting film or adjacent to the light redirecting film, such as between the adhesive layer and the back sheet, or between the base layer and the adhesive layer, or between the light redirecting film and the base layer.
  • the adhesive composition can perform an exothermic reaction in a lamination process for producing a solar cell module, thereby further crosslinking the adhesive layer so as to enhance the strength of the adhesive layer, maintain the adhesion force and form no weak points.
  • the term“exothermic amount” means a amount of heat (unit: J/g) released by per gram of an adhesive composition at a temperature of 95°C or more, unless otherwise specified.
  • the adhesive composition has an exothermic amount of 2 - 40 J/g.
  • the exothermic amount is less than 2 J/g, the amount of heat released during the aging process is too low to cause further crosslinking of the adhesive layer.
  • the exothermic amount is more than 40 J/g, the heat released in the adhesive layer system is excessive, the system cross-links excessively, resulting in wrinkles of the light redirecting layer after the lamination of the components, and the formation of bulges after high moisture-heat aging.
  • the adhesive composition comprises:
  • the adhesive composition contains a high content (90 to 98% by weight) of a resin base material as a base material.
  • the resin base material is usually used in the form of pellets.
  • the specific type of the resin base material is not particularly limited as long as the resin base material can continue to be crosslinked at an exothermic amount of 2 - 40 J/g.
  • the resin base material is one or more selected from a group consisting of an ethylene-vinyl acetate (EVA) copolymer, a polyolefin (PO) resin, polypropylene oxide (PP), polyvinyl butyral (PVB), a
  • EVA ethylene-vinyl acetate
  • PO polyolefin
  • PP polypropylene oxide
  • PVB polyvinyl butyral
  • TSV tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer
  • the adhesive composition comprises 90-98wt% of the resin base material.
  • the commercially available products of the resin base material that can be used in the present invention include: the Elvax ® series of EVA resins manufactured by DuPont Limited (for example, Elvax ® 150, Elvax ® 250, Elvax ® 260, Elvax ® PV 1300Z, and Elvax ® 3135SB); the EVA resins produced by Hanwa Company (for example, PV280, PV282, El 82 and E283F); the EVA resins of V5110J and 6110M produced by BASF; the polyolefin (POE) resins of 8842 and 7256 produced by Dow Company; and the polyolefin (POE) resins such as Tafmer DF605, Tafmer DF640, Tafmer DF740, Tafmer DF7350, Tafmer DF8200, Tafmer DF840 and Tafmer DF7350 produced by Mistuchem Company.
  • the Elvax ® series of EVA resins manufactured by DuPont Limited for
  • the term“melt flow index” in accordance with the present invention has a general definition of the term in the art. That is, the term“melt flow index” according to the present invention refers to a weight of grams (unit: g) of a polymer obtained by melting pellets of the polymer into a polymer fluid at a temperature of 190°C and a pressure of 2.16 kg and flowing the polymer fluid through a circular tube having a diameter of 2.095 mm.
  • the melt flow index (MFI) of a polymer feedstock is a very important processing parameter for characterizing the properties of the polymer.
  • MFI melt flow index
  • the adhesive composition of the invention is used to attach a light redirecting film to the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module.
  • the solar cell module comprises a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet disposed in a thickness direction of the solar cell module in turn, wherein the plurality of solar cells spaced apart from each other form an array, the array comprising a plurality of mutually parallel solar cell strings in the same plane perpendicular to the thickness direction, each of the solar cell strings being composed of a plurality of solar cells connected in series, a string gap is formed between each two adjacent solar cell strings, and a cell gap is formed between each two adjacent solar cells in each of the solar cell strings.
  • the light redirecting film according to the present invention functions to re-reflect the light incident through the string gaps and/or the cell strings (2-4 mm) onto the solar cell sheets to improve the power generation efficiency of the module.
  • the drift of the light redirecting film causes loss of light and whitening of the components, resulting in poor appearance.
  • the resin base material has a melt flow index (MFI) in a range of 10-30. According to the present invention, when the melt flow index (MFI) of the resin base material is less than 10, it is not easy to uniformly extrude the obtained adhesive composition to form a film layer.
  • the relative positional shift of the light redirecting film in the high-temperature lamination process can be effectively suppressed, so that the drifting degree is less than 0.5 mm.
  • the term“drifting degree” according to the present invention refers to a displacement value (unit: mm) of a light redirecting film with respect to an initial position after the light redirecting film is adhered to a substrate by an adhesive composition and subjected to high temperature lamination treatment.
  • the resin base material is an ethylene-vinyl acetate (EVA) copolymer.
  • the ethylene-vinyl acetate (EVA) copolymer is a polymer obtained by copolymerizing an ethylene monomer with vinyl acetate.
  • a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer (which is also referred to as“VA content”) is in a range of 24-30 wt%.
  • a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer( which is also referred to as“VA content”) is in a range of 26-28 wt%.
  • VA content is less than 24% by weight, the adhesiveness of the obtained adhesive composition to a substrate is deteriorated, and the transparency of the resulting material after lamination is also poor, which is disadvantageous for being applied to a double-sided double-glass assembly.
  • the VA content is more than 30% by weight, the film formed of the adhesive composition is too soft, resulting in wrinkle of the film.
  • the adhesive composition contains a peroxide crosslinking agent to promote the crosslinking reaction thereof.
  • a peroxide crosslinking agent is a very effective cross-linking agent, which generate alkyl radicals by pyrolysis, and the alkyl radicals generate polymer radicals by chain transferring reaction, and the polymer radicals are mutually cross-linked.
  • the peroxide crosslinking agent is one or more selected from a group consisting of benzoyl peroxide (BPO), dicumyl peroxide (DCP), t-amyl peroxyacetate (TAP A), tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH) or the like.
  • BPO benzoyl peroxide
  • DCP dicumyl peroxide
  • TAP A t-amyl peroxyacetate
  • TBEC tert-butyl peroxy-2-ethylhexyl carbonate
  • TPMH tert-butyl peroxy-3, 5, 5-trimethyl hexanoate
  • the adhesive composition comprises from 0.4 to 1.4% by weight of a peroxide crosslinking agent, based on the total weight of the adhesive composition.
  • a peroxide crosslinking agent which can be used in the present invention include: tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH) produced by Arkema Corporation.
  • the adhesive composition of the present invention comprises a non-peroxide crosslinking agent.
  • the non-peroxide crosslinking agents are compounds having multiple double bond functional groups that participate in cross-linking in the reaction. Due to the fast reaction rate, the low molecular weight products resulting from the coupling of the peroxide alkyl radicals and the polymer radicals are reduced.
  • the non-peroxide crosslinking agent is one or more selected from a group consisting of trimethylolpropane triacrylate (TMPTA) and triallyl isocyanurate (TAIC).
  • TMPTA trimethylolpropane triacrylate
  • TAIC triallyl isocyanurate
  • the adhesive composition comprises from 0.4 to 1.6% by weight of a non-peroxide crosslinking agent, based on the total weight of the adhesive composition.
  • the non-peroxide crosslinking agent may be a single component or may be a mixture of two or more components.
  • Specific examples of the non-peroxide crosslinking agent which can be used in the present invention include trimethylolpropane triacrylate (TMPTA) SR 351 and triallyl isocyanurate (TAIC) manufactured by Sartomer Corporation.
  • TMPTA trimethylolpropane triacrylate
  • TAIC triallyl isocyanurate
  • the adhesive composition contains a coupling agent.
  • the coupling agent is one or more selected from a group consisting of a silane coupling agent and a phthalic ester coupling agent.
  • the adhesive composition comprises from 0.5 to 1.5% by weight of a coupling agent, based on the total weight of the adhesive composition.
  • Specific products of the coupling agent which can be used in the present invention include Y-(methacryloyloxy)propyl trimethoxysilane manufactured by
  • the adhesive composition contains an ultraviolet absorber.
  • the ultraviolet absorber is one or more selected from a group consisting of a salicyl ester ultraviolet absorber, a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber and the like.
  • the salicyl ester ultraviolet absorber is one or more selected from a group consisting of methyl salicylate, ethyl salicylate and octyl salicylate.
  • the benzophenone ultraviolet absorber is one or more selected from a group consisting of 2-hydroxy -4-methoxybenzophenone and
  • the benzotriazole ultraviolet absorber is one or more selected from a group consisting of 2-(2’ -hydroxy-3’, 5’ -di-tert-phenyl)-5-chlorobenzotriazole and 2-(2’-hydroxy-5’-methylphenyl) benzotriazole.
  • the adhesive composition contains 0.5 to 4% by weight of the ultraviolet absorber based on the total weight of the adhesive composition. Specific products of the ultraviolet absorber which can be used in the present invention include:
  • the adhesive composition contains an ultraviolet stabilizer.
  • the ultraviolet stabilizer is a hindered amine ultraviolet stabilizer.
  • the hindered amine ultraviolet stabilizer is one or more selected from a group consisting of polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl-l-piperidineethanol) ester, poly[(6-morpholinyl-5-triazine-2,4-diyl) (2,2,6,6-tetramethylpiperidinyl)imino
  • the adhesive composition contains 0.2 to 2% by weight of the ultraviolet stabilizer based on the total weight of the adhesive composition.
  • Specific products of the ultraviolet stabilizer which can be used in the present invention include: polysuccinic acid
  • GW 540 under a name of GW 540; TINUVIN 770, TINUVIN 783, TINUVIN P, TINUVIN 788 produced by BASF Company; and CYASORB UV1164, CYASORB UV 2126, CYASORB UV 3853, CYASORB THT produced by Cytec Corporation; or the like.
  • the adhesive composition can be prepared by simple mixing and agitation. Specifically, particles of a resin base material are mixed with a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, a ultraviolet absorber, and a ultraviolet stabilizer, and optionally other components at room temperature (10°C-30°C) to obtain an adhesive composition.
  • a light redirecting film comprising a light redirecting layer, a base layer and a reactive adhesive layer in turn, wherein the reactive adhesive layer comprises the above adhesive composition.
  • the base layer has been subjected to a physical surface treatment.
  • the physical surface treatment is corona treatment or plasma treatment.
  • the reactive adhesive layer has a thickness in a range of 10-100 pm, preferably 20-50 pm.
  • the light redirecting layer comprises a plurality of microstructures that are orderly arranged and protruded from the base layer.
  • the light redirecting layer comprises a plurality of microstructures that are randomly arranged and protruded from the base layer.
  • microstructures comprises an array of abutting triangular prisms whose orientation direction is non-linearly oriented.
  • the term “an array of abutting triangular prisms” refers to an array comprising a plurality of triangular prisms arranged side by side.
  • each triangular prism in the array of abutting triangular prisms is a triangular prism having an apex angle being 120 degrees toward the solar cells and two base angles being 30 degrees respectively.
  • the sharp peak of at least one triangular prism in the array of abutting triangular prisms toward the solar cells may be replaced by a round peak.
  • the round peak of the at least one triangular prism in the array of abutting triangular prisms has a radius of curvature of from 0.2 micron to 5 microns.
  • the plurality of microstructures comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane.
  • the light redirecting film further comprises a primer layer between the reactive adhesive layer and the base layer. The primer layer functions to enhance the adhesion between the adhesive layer and the base layer to prevent the delamination between the adhesive layer and the base layer.
  • the primer layer is a polyester primer layer or a polyacrylate primer layer.
  • the light redirecting film further comprises a light reflecting layer, wherein the light reflecting layer covers the plurality of microstructures and conforms to the plurality of microstructures.
  • Fig. 1 shows a cross-sectional view of a light redirecting film 1 according to an embodiment of the invention.
  • the light redirecting film 1 comprises a light redirecting layer 2, a base layer 3 and a reactive adhesive layer 4 in turn, wherein the reactive adhesive layer 4 comprises the above adhesive composition.
  • the reactive adhesive layer 4 has a thickness in a range of 10-100 pm, preferably 20-50 pm . When the thickness of the reactive adhesive layer 4 is greater than 100 pm, the light guide film is liable to undergo relative positional drift during high temperature lamination process.
  • the light redirecting layer 2 comprises a plurality of microstructures 5 that are orderly arranged and protruded from the base layer.
  • the plurality of microstructures 5 that are orderly arranged and protruded from the base layer comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane.
  • Fig. 2 shows a perspective view of an array 6 of parallel triangular prisms included in a light redirecting film 1 according to an embodiment of the invention.
  • the light redirecting film 4 comprises an array 6 of parallel triangular prisms wherein one quadrilateral plane of each triangular prism 7 is in the same plane 8.
  • D is the orientation direction of array 6 of parallel triangular prisms.
  • the light redirecting film 1 further comprises a primer layer 9 between the reactive adhesive layer 4 and the base layer 3.
  • the primer layer 9 comprises a polyester primer layer or a polyacrylate primer layer.
  • the light redirecting film 1 further comprises a light reflecting layer 10, wherein the light reflecting layer covers the plurality of microstructures 5 and conforms to the plurality of microstructures 5.
  • a solar cell module comprising a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet sequentially disposed along a thickness direction of the solar cell module, wherein the solar cell module further includes the above light redirecting film, which is provided between the post encapsulation layer and the back sheet and adheres to a surface of the back sheet through the reactive adhesive layer.
  • Fig. 3 shows a cross-sectional view of a solar cell module 11 according to an embodiment of the invention.
  • the solar cell module 11 comprises a light transmissive element 12, a front encapsulation layer 13, a plurality of solar cells 14 spaced apart from each other, a post encapsulation layer 15, and a back sheet 16 sequentially disposed along a thickness direction T of the solar cell module 11, wherein the solar cell module 11 further includes the above light redirecting film 1, which is provided between the post encapsulation layer 15 and the back sheet 16 and adheres to a surface 17 of the back sheet 16 through the reactive adhesive layer 4.
  • the inventors of the present invention found that when the inner layer of the back sheet (i.e., the side facing the solar cells) contains a non-hot melt adhesive material or a fluorine-containing material (for example, a Kpf back sheet manufactured by Saiwu Company or a TFB back sheet manufactured by Zhonglai Company), it is especially prone to create bulges between the back sheet and the light redirecting film under aging conditions.
  • a non-hot melt adhesive material or a fluorine-containing material for example, a Kpf back sheet manufactured by Saiwu Company or a TFB back sheet manufactured by Zhonglai Company
  • Testing pieces were prepared from the various adhesive compositions prepared in the examples and comparative examples below according to the method for preparing an adhesive layer and a testing piece listed below.
  • the adhesive compositions prepared in the examples and comparative examples below were extruded respectively at 80-100°C onto a surface of a polyethylene terephthalate film having a thickness of 15 pm using a single-screw extruder manufactured by Kingwell Corporation to form a reactive adhesive film having a thickness of 35 pm.
  • the light redirecting film having the reactive adhesive film as mentioned above was cut into narrow strips of 5 mm width and 25 cm length. A strip was heat-applied to a side of a Kpf back sheet manufactured by Savigne Company at a speed of 5-10 cm/sec at 100°C.
  • a light-transmitting member (a XYG Model glass manufactured by Shine Separation Co., Ltd.), two EVA encapsulating films (EVA encapsulating films of 9100T and 9210B manufactured by 3M Innovation Co., Ltd.), and the back sheet with a light redirecting film having the reactive adhesive film as prepared above are laminated in a manner that the light redirecting film faced to the EVA encapsulating films to obtain a laminate.
  • the laminate was placed in a KRA-Y1322 laminator manufactured by Qinhuangdao Kezhirui Technology Co., Ltd., and vacuumed at a laminating temperature of 145°C for 5 minutes, then pressurized for 30 seconds and heated for 13 minutes to obtain a testing piece.
  • the reactive adhesive films and testing pieces obtained as above were tested for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree or the like according to the specific methods listed below.
  • the testing pieces obtained above were placed respectively in a Cl 000 environmental testing chamber manufactured by Envirotronics Company, and taken out after being kept at 85°C/85% humidity for 1000 hours.
  • the back sheet side and glass side of the testing pieces were observed by naked eyes to determine if there was bulging, foaming and delamination. If the above phenomenon existed, it is considered that the moisture-heat aging resistance is poor; and if the above phenomenon was not present, the moisture-heat aging resistance is considered to be eligible (Pass).
  • the heat capacity and heat flow of the reactive adhesive films prepared in the examples and comparative examples were directly measured respectively by using a differential scanning calorimeter having a model of Q2000 manufactured by TA Corporation in a temperature range of 20-220 C at a heating rate 10°C/min in nitrogen atmosphere.
  • the exothermic amount (J/g) and the exothermic temperature (°C) were calculated from the obtained DSC curve.
  • the laminated test pieces were tested respectively for bonding strength (unit: N/cm) between the polymer adhesive layer and the back sheet using an electronic universal testing machine with a model of 5969 manufactured by Instron Company according to ASTM D1876. According to this testing performance, the higher the bonding strength was preferable, and the adhesion performance was superior when the bonding strength is more than 40 N/cm.
  • the adhesive compositions prepared in the examples and the comparative examples were respectively extruded on a light redirecting film (T81 Model manufactured by 3M Co.) to obtain a light redirecting film having a reactive adhesive layer having a thickness of 25 pm.
  • the light guiding film was cut into film pieces having a width of 5 mm and a length of 25 cm.
  • a film piece was heat-applied to a textured surface of a XYG Model solar glass produced by Xinyi Glass Company to obtain a solar glass having a light redirecting film. Then, the profile of the light redirecting film on the solar glass was drawn with a marker.
  • a light-transmitting member an XYG Model glass manufactured by Shine Separation Co., Ltd.
  • EVA encapsulating films of 9100T and 9210B manufactured by 3M Co. two EVA encapsulating films
  • the solar glass having a light redirecting film as prepared above are laminated to obtain a laminate.
  • the laminate was placed in a KRA-Y1322 laminator manufactured by Qinhuangdao Kezhirui Technology Co., Ltd., and vacuumed at a laminating temperature of 145°C for 5 minutes, then pressurized for 30 seconds and heated for 13 minutes to obtain a testing piece.
  • the relative distance between the position of the light redirecting film on the laminated testing piece and the profile drawn by the original marker was measured and regarded as a drifting degree (unit: mm).
  • the light redirecting film is considered to be acceptable when the drifting degree is less than 0.5 mm.
  • the resin pellets EVA 1, the peroxide crosslinking agent 1, the non-peroxide crosslinking agent 1, the coupling agent 1, the ultraviolet absorber 1 and the ultraviolet stabilizer 2 were mixed and uniformly stirred at room temperature to obtain an adhesive composition 1.
  • the content of the resin pellets EVA 1 was 95.2% by weight
  • the content of the peroxide crosslinking agent 1 was 1.4% by weight
  • the content of the non-peroxide crosslinking agent 1 was 0.4% by weight
  • the content of the coupling agent 1 was 1% by weight
  • the content of the ultraviolet absorber 1 was 1% by weight
  • the content of the ultraviolet stabilizer 2 was 1% by weight.
  • a reactive adhesive film 1 was prepared from the adhesive composition 1 according to the method for producing a reactive adhesive film as described above.
  • a testing piece 1 was prepared from the reactive adhesive film 1 according to the method for preparing a testing piece as described above.
  • the adhesive composition 1, the reactive adhesive film 1 and the testing piece 1 were subjected to the tests for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree according to the specific methods listed above, and the testing results thereof are shown in Table 2.
  • Examples 2-9 and Comparative Examples 1-6 were carried out in the same manner as shown in Example 1, except that the kinds, presence or absence and content of each component were changed as shown in Table 2 to obtain respective adhesive combinations.
  • Respective reactive adhesive films were prepared from the adhesive compositions obtained in Examples 2-9 and Comparative Examples 1-6 according to the method for producing a reactive adhesive film as described above.
  • Respective testing pieces were prepared from the respective reactive adhesive films according to the method for preparing a testing piece as described above.
  • the respective adhesive compositions, reactive adhesive films and testing pieces were subjected to the tests for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree according to the specific methods listed above, and the testing results thereof are shown in Tables 2 and 3.
  • Comparative Example 1 was carried out under the similar conditions as Example 1, except that the adhesive composition of Comparative Example 1 comprised no non-peroxide crosslinking agent. As can be seen from Tables 2 and 3 above, when the adhesive composition of
  • Comparative Example 1 comprised no non-peroxide crosslinking agent, a low molecular weight product resulting from the coupling of peroxyalkyl radicals and polymer radicals may be present in the adhesive composition system, thereby the bonding strength of the polymer adhesive film was significantly lowered, and the phenomenon of bulging, foaming, and delamination of the light guiding film were observed.
  • the adhesive composition system comprised no peroxide crosslinking agent and no non-peroxide crosslinking agent.
  • the adhesive composition did not undergo an exothermic reaction at a temperature of 95°C or more and released no heat.
  • the reactive adhesive film did not undergo further crosslinking reaction, resulting in bulges in the light redirecting film and the bonding strength thereof was reduced.
  • Comparative Example 4 the amount of the non-peroxide crosslinking agent present in the adhesive composition system was excessive (1.8% by weight), resulting in an excessive exothermic amount of 46 J/g.
  • the excessive exothermic amount caused the shrinkage of the adhesive film to become high and partial wrinkles were generated during application, which was disadvantageous to the appearance of the module and bulges also appeared in the wrinkle portions.
  • the adhesive composition system of Comparative Example 5 comprised a resin base material of EVA2.
  • the melt flow index (MFI) of the resin base material of EVA2 was larger (that is, 40).
  • MFI melt flow index
  • the results thereof showed that, although the bonding strength is high, the light redirecting film on the testing piece exhibited a very significant drift (that is, a drift degree greater than 1 mm) and poor moisture-heat aging resistance wherein bulges were formed in the light redirecting film.
  • the adhesive composition system of Comparative Example 6 comprised a resin base material of EVA3. As shown in Table 1, the VA content of the resin base material of EVA3 was smaller (only 20% by weight). As a result, the bonding strength was lowered, and the phenomenon of bulging, foaming, and delamination was observed.

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Abstract

An adhesive composition comprises a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction at a temperature of 95°C or more and has an exothermic amount of 2-40 J/g. The invention further provides a light redirecting film which comprises a reactive adhesive layer comprising the adhesive composition. Furthermore, the invention further provides a solar cell module comprising the light redirecting film. When the adhesive composition according to the present invention is used as an adhesive layer for adhering a light redirecting film to a back sheet during the assembly of a solar cell module, the formation of bulges in the adhesive layer during high moisture-heat aging may be avoided while maintaining the high adhesion of the adhesive layer, and the relative positional drift of the light redirecting film during the high temperature laminating process may be greatly reduced.

Description

ADHESIVE COMPOSITION. LIGHT REDIRECTING FILM AND SOLAR CELL
MODULE
TECHNICAL FIELD
The invention relates to the technical field of photovoltaic cells, in particular to an adhesive composition, and a light redirecting film and a solar cell module comprising the same.
BACKGROUND
With the gradual increase of environmental problems, the development and application of clean energies are becoming more and more urgent. Solar energy has received more and more attention as a clean energy source. A solar cell is a device that uses solar energy to generate electricity.
Currently, the common solar cells include a battery body that is encapsulated in an encapsulation cover and an encapsulation back sheet. Light is incident on the light-facing surface of the battery body through the encapsulation cover, and the battery body converts the light energy in the light into electrical energy. In order to improve the power generation efficiency of a solar cell module, a light redirecting film may be provided inside the solar cell module. When power is generated by the solar cell module, a light may be irradiated onto an optical structure of the light redirecting film after passing through a light transmissive element. The optical structure of the light redirecting film can reflect the incident light and change the direction thereof. Since the light is incident from top to bottom, the light redirecting film reflects the light upward toward the light transmissive element. When the light reflected by the light redirecting film enters the light transmissive element and propagates into the interface between the light transmissive element and air, the light is reflected and the direction of light propagation changes again, and finally the light-facing surfaces of the solar cells are illuminated by the light. Since the solar cells use the light to generate electricity, the power generation efficiency is improved. The light redirecting film is usually disposed on the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module by an adhesive layer. However, in a high-temperature and high-humidity environment, the adhesive layer gradually ages over time, and bulges are generated between the light redirecting film and the package back sheet, thereby causing the light redirecting film to be broken or fall off from the adhering surface.
Therefore, it has been important to develop an adhesive material having good
moisture-heat aging resistance for a solar cell module. SUMMARY OF THE INVENTION
In view of the technical problem set forth above, an object of the present invention is to provide an adhesive material having good moisture-heat aging resistance for a solar cell module, which has high adhesion and does not produce bulges in the adhesive layer under a moisture-heat aging condition.
According to one aspect of the invention, there provides an adhesive composition comprising a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction at a temperature of 95°C or more and has an exothermic amount of 2-40 J/g.
According to certain preferable embodiments of the invention, in terms of the total weight of the adhesive composition,
90-98wt% of the resin base material;
0.4-1.4wt% of the peroxide crosslinking agent;
0.4-1.6wt% of the non-peroxide crosslinking agent;
0.5-1.5wt% of the coupling agent;
0.5-4wt% of the ultraviolet absorber; and
0.2-2wt% of the ultraviolet stabilizer.
According to certain preferable embodiments of the invention, the resin base material is one or more selected from a group consisting of an ethylene-vinyl acetate (EVA) copolymer, a polyolefin (PO) resin, polypropylene oxide (PP), polyvinyl butyral (PVB), a
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) copolymer, an
ethyl ene-tetrafluoroethylene (ETFE) copolymer, polyvinylidene fluoride (PVDF), polyurethane (PU), polymethylmethacrylate (PMMA) and polyimide (PI).
According to certain preferable embodiments of the invention, the resin base material has a melt flow index (MFI) in a range of 10-30.
According to certain preferable embodiments of the invention, the resin base material is an ethylene-vinyl acetate (EVA) copolymer.
According to certain preferable embodiments of the invention, in terms of the total weight of the ethylene- vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 24-30 wt%. According to certain preferable embodiments of the invention, in terms of the total weight of the ethylene- vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 26-28 wt%.
According to certain preferable embodiments of the invention, the peroxide crosslinking agent is one or more selected from a group consisting of benzoyl peroxide (BPO), dicumyl peroxide (DCP), t-amyl peroxyacetate (TAP A), tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH).
According to certain preferable embodiments of the invention, the non-peroxide crosslinking agent is one or more selected from a group consisting of trimethylolpropane triacrylate (TMPTA) and triallyl isocyanurate (TAIC).
According to certain preferable embodiments of the invention, the coupling agent is one or more selected from a group consisting of a silane coupling agent and a phthalic ester coupling agent.
According to certain preferable embodiments of the invention, the ultraviolet absorber is one or more selected from a group consisting of a salicyl ester ultraviolet absorber, a
benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber.
According to certain preferable embodiments of the invention, the salicyl ester ultraviolet absorber is one or more selected from a group consisting of methyl salicylate, ethyl salicylate and octyl salicylate.
According to certain preferable embodiments of the invention, the benzophenone ultraviolet absorber is one or more selected from a group consisting of
2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-n-octyloxybenzophenone.
According to certain preferable embodiments of the invention, the benzotriazole ultraviolet absorber is one or more selected from a group consisting of
2-(2’ -hydroxy-3’, 5’-di-tert-phenyl)-5-chlorobenzotriazole and 2-(2’-hydroxy-5’-methylphenyl) benzotriazole.
According to certain preferable embodiments of the invention, the ultraviolet stabilizer is a hindered amine ultraviolet stabilizer.
According to certain preferable embodiments of the invention, the hindered amine ultraviolet stabilizer is one or more selected from a group consisting of polysuccinic acid
(4-hydroxy-2,2,6,6-tetramethyl- 1 -piperidineethanol) ester, poly[(6-morpholinyl-5-triazine-2,4-diyl) (2,2,6,6-tetramethylpiperidinyl)imino
hexamethylene[(2,2,6,6-tetramethylpiperidyl)-imino]],
4-benzoyloxy-2,2,6,6-tetramethylpiperidine and tris(l,2,2,6,6-pentapiperidinyl) phosphite.
According to another aspect of the invention, there provides a light redirecting film, comprising a light redirecting layer, a base layer and a reactive adhesive layer in turn, wherein the reactive adhesive layer comprises the above adhesive composition.
According to certain preferable embodiments of the invention, the base layer has been subjected to a physical surface treatment.
According to certain preferable embodiments of the invention, the physical surface treatment is corona treatment or plasma treatment.
According to certain preferable embodiments of the invention, the reactive adhesive layer has a thickness in a range of 10-100 pm.
According to certain preferable embodiments of the invention, the light redirecting layer comprises a plurality of microstructures that are orderly arranged and protruded from the base layer.
According to certain preferable embodiments of the invention, the light redirecting layer comprises a plurality of microstructures that are randomly arranged and protruded from the base layer.
According to certain preferable embodiments of the invention, the plurality of microstructures comprises an array of abutting triangular prisms whose orientation direction is non-linearly oriented.
According to certain preferable embodiments of the invention, the plurality of microstructures comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane.
According to certain preferable embodiments of the invention, the light redirecting film further comprises a primer layer between the reactive adhesive layer and the base layer.
According to certain preferable embodiments of the invention, the primer layer is a polyester primer layer or a polyacrylate primer layer.
According to certain preferable embodiments of the invention, the light redirecting film further comprises a light reflecting layer, wherein the light reflecting layer covers the plurality of microstructures and conforms to the plurality of microstructures. According to a further aspect of the invention, there provides a solar cell module comprising a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet sequentially disposed along a thickness direction of the solar cell module, wherein the solar cell module further includes the above light redirecting film, which is provided between the post encapsulation layer and the back sheet and adheres to a surface of the back sheet through the reactive adhesive layer.
According to certain preferable embodiments of the invention, a side of the back sheet facing the solar cells comprises a non-hot melt adhesive material.
According to certain preferable embodiments of the invention, a side of the back sheet facing the solar cells comprises a fluorine-containing material.
The advantages of the present invention include:
1. The adhesive layer has high adhesion;
2. The formation of bulges between the light redirecting film and the package back sheet during high moisture-heat aging is avoided; and
3. The relative positional drift of the light redirecting film during the high temperature laminating process for the solar cell module may be greatly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a cross-sectional view of a light redirecting film according to an embodiment of the invention;
Fig. 2 shows a perspective view of an array of parallel triangular prisms included in a light redirecting film according to an embodiment of the invention; and
Fig. 3 shows a cross-sectional view of a solar cell module according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. It will be appreciated that other embodiments may be practiced without departing from the scope of the invention. Therefore, the following detailed description is non-limiting.
All numbers indicating the sizes, quantities, and physicochemical properties of a feature used in the specification and claims, unless otherwise indicated, are understood to be modified in all instances by the term“about”. Accordingly, the numerical parameters set forth in the above description and the appended claims are approximations unless otherwise indicated, and those skilled in the field are able to use the teachings disclosed herein. The range of values defined by endpoints includes all numbers in the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, or the like.
During the assembly of a solar cell module, a light redirecting film is usually disposed on the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module by an adhesive layer. However, in a high-temperature and high-humidity environment, the adhesive layer gradually ages over time, and bulges are generated between the light redirecting film and the package back sheet, thereby causing the light redirecting film to be broken or fall off from the adhering surface.
According to one aspect of the invention, there provides an adhesive composition comprising a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction in a lamination process for producing a solar cell module (generally, a lamination temperature of 140°C or higher) and has an exothermic amount of 2-40 J/g.
Without wishing to be bound by theory, it is believed that the reason for the formation of bulges that can be discerned by naked eyes between the light redirecting film and the back sheet during the moisture-heat aging of the adhesive layer is as follows. Under aging conditions (for example, 85°C / 85% humidity), the resin in the adhesive layer softens and melts, resulting in a decrease in adhesion to the light redirecting film and the back sheet. At the same time, the water vapor in the environment and small molecular gases in the module will accumulate at a position having a weak bonding force to form bulges. The bulges may be formed anywhere within the light redirecting film or adjacent to the light redirecting film, such as between the adhesive layer and the back sheet, or between the base layer and the adhesive layer, or between the light redirecting film and the base layer. According to the invention, by specifically selecting the specific components and the contents thereof in the adhesive composition, the adhesive composition can perform an exothermic reaction in a lamination process for producing a solar cell module, thereby further crosslinking the adhesive layer so as to enhance the strength of the adhesive layer, maintain the adhesion force and form no weak points.
According to the disclosure of the present application, the term“exothermic amount” means a amount of heat (unit: J/g) released by per gram of an adhesive composition at a temperature of 95°C or more, unless otherwise specified. The adhesive composition has an exothermic amount of 2 - 40 J/g. When the exothermic amount is less than 2 J/g, the amount of heat released during the aging process is too low to cause further crosslinking of the adhesive layer. On the other hand, when the exothermic amount is more than 40 J/g, the heat released in the adhesive layer system is excessive, the system cross-links excessively, resulting in wrinkles of the light redirecting layer after the lamination of the components, and the formation of bulges after high moisture-heat aging.
Preferably, in terms of the total weight of the adhesive composition, the adhesive composition comprises:
90-98wt% of the resin base material;
0.4-1.4wt% of the peroxide crosslinking agent;
0.4-1.6wt% of the non-peroxide crosslinking agent;
0.5-1.5wt% of the coupling agent;
0.5-4wt% of the ultraviolet absorber; and
0.2-2wt% of the ultraviolet stabilizer.
According to the technical solution of the present application, the adhesive composition contains a high content (90 to 98% by weight) of a resin base material as a base material. The resin base material is usually used in the form of pellets. The specific type of the resin base material is not particularly limited as long as the resin base material can continue to be crosslinked at an exothermic amount of 2 - 40 J/g. Preferably, the resin base material is one or more selected from a group consisting of an ethylene-vinyl acetate (EVA) copolymer, a polyolefin (PO) resin, polypropylene oxide (PP), polyvinyl butyral (PVB), a
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) copolymer, an
ethyl ene-tetrafluoroethylene (ETFE) copolymer, polyvinylidene fluoride (PVDF), polyurethane (PEI), polymethylmethacrylate (PMMA) and polyimide (PI). In terms of the total weight of the adhesive composition, the adhesive composition comprises 90-98wt% of the resin base material. The commercially available products of the resin base material that can be used in the present invention include: the Elvax® series of EVA resins manufactured by DuPont Limited (for example, Elvax® 150, Elvax® 250, Elvax® 260, Elvax® PV 1300Z, and Elvax® 3135SB); the EVA resins produced by Hanwa Company (for example, PV280, PV282, El 82 and E283F); the EVA resins of V5110J and 6110M produced by BASF; the polyolefin (POE) resins of 8842 and 7256 produced by Dow Company; and the polyolefin (POE) resins such as Tafmer DF605, Tafmer DF640, Tafmer DF740, Tafmer DF7350, Tafmer DF8200, Tafmer DF840 and Tafmer DF7350 produced by Mistuchem Company.
Unless otherwise specified, the term“melt flow index” in accordance with the present invention has a general definition of the term in the art. That is, the term“melt flow index” according to the present invention refers to a weight of grams (unit: g) of a polymer obtained by melting pellets of the polymer into a polymer fluid at a temperature of 190°C and a pressure of 2.16 kg and flowing the polymer fluid through a circular tube having a diameter of 2.095 mm.
The melt flow index (MFI) of a polymer feedstock is a very important processing parameter for characterizing the properties of the polymer. The higher the melt flow index (MFI) is, the better the fluidity of the polymer and the easier it is to be processed. However, it has been found by the inventors that for the application of the present invention, the light redirecting film produced from a polymer having a higher melt flow index is liable to drift after the lamination process for producing a solar cell module at high temperature. The adhesive composition of the invention is used to attach a light redirecting film to the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module. The solar cell module comprises a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet disposed in a thickness direction of the solar cell module in turn, wherein the plurality of solar cells spaced apart from each other form an array, the array comprising a plurality of mutually parallel solar cell strings in the same plane perpendicular to the thickness direction, each of the solar cell strings being composed of a plurality of solar cells connected in series, a string gap is formed between each two adjacent solar cell strings, and a cell gap is formed between each two adjacent solar cells in each of the solar cell strings. The light redirecting film according to the present invention functions to re-reflect the light incident through the string gaps and/or the cell strings (2-4 mm) onto the solar cell sheets to improve the power generation efficiency of the module. However, the drift of the light redirecting film causes loss of light and whitening of the components, resulting in poor appearance. Preferably, the resin base material has a melt flow index (MFI) in a range of 10-30. According to the present invention, when the melt flow index (MFI) of the resin base material is less than 10, it is not easy to uniformly extrude the obtained adhesive composition to form a film layer. According to the present invention, when the melt flow index (MFI) of the resin base material is in the range of 10 to 30, the relative positional shift of the light redirecting film in the high-temperature lamination process can be effectively suppressed, so that the drifting degree is less than 0.5 mm. The term“drifting degree” according to the present invention refers to a displacement value (unit: mm) of a light redirecting film with respect to an initial position after the light redirecting film is adhered to a substrate by an adhesive composition and subjected to high temperature lamination treatment.
In order to achieve the technical effect of the present invention, preferably, the resin base material is an ethylene-vinyl acetate (EVA) copolymer. The ethylene-vinyl acetate (EVA) copolymer is a polymer obtained by copolymerizing an ethylene monomer with vinyl acetate. Preferably, in terms of the total weight of the ethylene-vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer (which is also referred to as“VA content”) is in a range of 24-30 wt%. More preferably, in terms of the total weight of the ethylene-vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer( which is also referred to as“VA content”) is in a range of 26-28 wt%. When the VA content is less than 24% by weight, the adhesiveness of the obtained adhesive composition to a substrate is deteriorated, and the transparency of the resulting material after lamination is also poor, which is disadvantageous for being applied to a double-sided double-glass assembly. On the other hand, when the VA content is more than 30% by weight, the film formed of the adhesive composition is too soft, resulting in wrinkle of the film.
By adjusting the specific content of the repeating units derived from vinyl acetate to the range of 24 to 30% by weight, it is possible to improve the bonding strength and the moisture-heat aging resistance of the adhesive composition.
According to a technical solution of the present invention, the adhesive composition contains a peroxide crosslinking agent to promote the crosslinking reaction thereof. In the art, a peroxide crosslinking agent is a very effective cross-linking agent, which generate alkyl radicals by pyrolysis, and the alkyl radicals generate polymer radicals by chain transferring reaction, and the polymer radicals are mutually cross-linked. There is no limitation on the specific kind of the peroxide crosslinking agent which can be used in the present invention, and preferably, the peroxide crosslinking agent is one or more selected from a group consisting of benzoyl peroxide (BPO), dicumyl peroxide (DCP), t-amyl peroxyacetate (TAP A), tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH) or the like. The addition of a peroxide crosslinking agent to the adhesive composition is effective to increase the crosslinking degree of the product, thereby increasing the bulk strength and tackiness of the polymer. However, in the lamination process for producing a solar cell module, if the peroxide crosslinking agent is added too much and cannot be completely reacted, it will be slowly decomposed during use to generate a gas, resulting in bulges in the adhesive layer. The adhesive composition comprises from 0.4 to 1.4% by weight of a peroxide crosslinking agent, based on the total weight of the adhesive composition. Specific examples of the peroxide crosslinking agent which can be used in the present invention include: tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH) produced by Arkema Corporation.
According to a technical solution of the present invention, a lower concentration of a peroxide crosslinking agent is employed. In order to ensure a higher crosslinking degree at lower concentration of the peroxide crosslinking agent to achieve the desired bond strength and moisture-heat aging resistance, the adhesive composition of the present invention comprises a non-peroxide crosslinking agent. The non-peroxide crosslinking agents are compounds having multiple double bond functional groups that participate in cross-linking in the reaction. Due to the fast reaction rate, the low molecular weight products resulting from the coupling of the peroxide alkyl radicals and the polymer radicals are reduced. There is no limitation on the specific kind of the non-peroxide crosslinking agent which can be used in the present invention, and preferably, the non-peroxide crosslinking agent is one or more selected from a group consisting of trimethylolpropane triacrylate (TMPTA) and triallyl isocyanurate (TAIC). When the content of the non-peroxide crosslinking agent is too high, the shrinkage rate of the film (i.e., the adhesive layer) becomes high, and partial wrinkles of the film are generated during application, which is disadvantageous to the appearance of the component, and the pleated portion is also prone to bulging. Preferably, the adhesive composition comprises from 0.4 to 1.6% by weight of a non-peroxide crosslinking agent, based on the total weight of the adhesive composition. The non-peroxide crosslinking agent may be a single component or may be a mixture of two or more components. Specific examples of the non-peroxide crosslinking agent which can be used in the present invention include trimethylolpropane triacrylate (TMPTA) SR 351 and triallyl isocyanurate (TAIC) manufactured by Sartomer Corporation.
According to a technical solution of the present invention, the adhesive composition contains a coupling agent. Preferably, the coupling agent is one or more selected from a group consisting of a silane coupling agent and a phthalic ester coupling agent. Preferably, the adhesive composition comprises from 0.5 to 1.5% by weight of a coupling agent, based on the total weight of the adhesive composition. Specific products of the coupling agent which can be used in the present invention include Y-(methacryloyloxy)propyl trimethoxysilane manufactured by
Momentive Company under a product name of A174 and 3-aminopropyl tri ethoxy silane manufactured by Momentive Company under a product name of A1100.
According to a technical solution of the present invention, the adhesive composition contains an ultraviolet absorber. Preferably, the ultraviolet absorber is one or more selected from a group consisting of a salicyl ester ultraviolet absorber, a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber and the like. The salicyl ester ultraviolet absorber is one or more selected from a group consisting of methyl salicylate, ethyl salicylate and octyl salicylate. The benzophenone ultraviolet absorber is one or more selected from a group consisting of 2-hydroxy -4-methoxybenzophenone and
2-hydroxy-4-n-octyloxybenzophenone. The benzotriazole ultraviolet absorber is one or more selected from a group consisting of 2-(2’ -hydroxy-3’, 5’ -di-tert-phenyl)-5-chlorobenzotriazole and 2-(2’-hydroxy-5’-methylphenyl) benzotriazole. The adhesive composition contains 0.5 to 4% by weight of the ultraviolet absorber based on the total weight of the adhesive composition. Specific products of the ultraviolet absorber which can be used in the present invention include:
2-hydroxy-4-n-octyloxybenzophenone produced by BASF Corporation under a product name of Chimassorb® 81; and 2-(2,-hydroxy-3,,5’-di-tert-phenyl)-5-chlorobenzotriazole produced by BASF Corporation under a product name of UVP 327.
According to a technical solution of the present invention, the adhesive composition contains an ultraviolet stabilizer. Preferably, the ultraviolet stabilizer is a hindered amine ultraviolet stabilizer. Preferably, the hindered amine ultraviolet stabilizer is one or more selected from a group consisting of polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl-l-piperidineethanol) ester, poly[(6-morpholinyl-5-triazine-2,4-diyl) (2,2,6,6-tetramethylpiperidinyl)imino
hexamethylene[(2,2,6,6-tetramethylpiperidyl)-imino]],
4-benzoyloxy-2,2,6,6-tetramethylpiperidine and tris(l,2,2,6,6-pentapiperidinyl) phosphite. The adhesive composition contains 0.2 to 2% by weight of the ultraviolet stabilizer based on the total weight of the adhesive composition. Specific products of the ultraviolet stabilizer which can be used in the present invention include: polysuccinic acid
(4-hydroxy-2,2,6,6-tetramethyl-l-piperidineethanol) ester manufactured by BASF under a product name of TINUVIN 622; poly[(6-morpholinyl-5-triazine-2,4-diyl)
(2,2,6,6-tetramethylpiperidinyl)imino hexamethylene[(2,2,6,6-tetramethylpiperidyl)-imino]] produced by Cytec Corporation under a name of CYASORB UV3346; 4-benzoyloxy-2,2,6,6-tetramethyl piperidine produced by Guangdong Light Stabilizer Co., Ltd. under a name of 744; tris(l,2,2,6,6-pentapiperidinyl) phosphite produced by Hubei Jusheng Technology Co., Ltd. under a name of GW 540; TINUVIN 770, TINUVIN 783, TINUVIN P, TINUVIN 788 produced by BASF Company; and CYASORB UV1164, CYASORB UV 2126, CYASORB UV 3853, CYASORB THT produced by Cytec Corporation; or the like.
There is no particular limitation on the method of preparing the adhesive composition according to the present invention. Typically, the adhesive composition can be prepared by simple mixing and agitation. Specifically, particles of a resin base material are mixed with a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, a ultraviolet absorber, and a ultraviolet stabilizer, and optionally other components at room temperature (10°C-30°C) to obtain an adhesive composition.
According to another aspect of the invention, there provides a light redirecting film, comprising a light redirecting layer, a base layer and a reactive adhesive layer in turn, wherein the reactive adhesive layer comprises the above adhesive composition. In order to enhance the adhesion between the adhesive layer and the base layer to prevent delamination between the adhesive layer and the base layer, it is preferred that the base layer has been subjected to a physical surface treatment. The physical surface treatment is corona treatment or plasma treatment. In order to provide sufficient adhesion to adhere a light redirecting film on the back surfaces of the solar cells or on a surface of the back sheet inside the solar cell module, the reactive adhesive layer has a thickness in a range of 10-100 pm, preferably 20-50 pm. Optionally, the light redirecting layer comprises a plurality of microstructures that are orderly arranged and protruded from the base layer. Optionally, the light redirecting layer comprises a plurality of microstructures that are randomly arranged and protruded from the base layer. Optionally, the plurality of
microstructures comprises an array of abutting triangular prisms whose orientation direction is non-linearly oriented. According to certain preferable embodiments of the invention, the term “an array of abutting triangular prisms” refers to an array comprising a plurality of triangular prisms arranged side by side. According to certain preferable embodiments of the invention, each triangular prism in the array of abutting triangular prisms is a triangular prism having an apex angle being 120 degrees toward the solar cells and two base angles being 30 degrees respectively. Optionally, the sharp peak of at least one triangular prism in the array of abutting triangular prisms toward the solar cells may be replaced by a round peak. Preferably, the round peak of the at least one triangular prism in the array of abutting triangular prisms has a radius of curvature of from 0.2 micron to 5 microns. Optionally, the plurality of microstructures comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane. Preferably, the light redirecting film further comprises a primer layer between the reactive adhesive layer and the base layer. The primer layer functions to enhance the adhesion between the adhesive layer and the base layer to prevent the delamination between the adhesive layer and the base layer. In addition to achieving this technical effect with the primer layer, it is also possible to use a method of subjecting the base layer to corona treatment to enhance the adhesion between the adhesive layer and the base layer to prevent the base layer from being delaminated from the adhesive layer. Preferably, the primer layer is a polyester primer layer or a polyacrylate primer layer. The light redirecting film further comprises a light reflecting layer, wherein the light reflecting layer covers the plurality of microstructures and conforms to the plurality of microstructures.
Specifically, Fig. 1 shows a cross-sectional view of a light redirecting film 1 according to an embodiment of the invention. The light redirecting film 1 comprises a light redirecting layer 2, a base layer 3 and a reactive adhesive layer 4 in turn, wherein the reactive adhesive layer 4 comprises the above adhesive composition. The reactive adhesive layer 4 has a thickness in a range of 10-100 pm, preferably 20-50 pm . When the thickness of the reactive adhesive layer 4 is greater than 100 pm, the light guide film is liable to undergo relative positional drift during high temperature lamination process. The light redirecting layer 2 comprises a plurality of microstructures 5 that are orderly arranged and protruded from the base layer. In one embodiment, the plurality of microstructures 5 that are orderly arranged and protruded from the base layer comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane. Fig. 2 shows a perspective view of an array 6 of parallel triangular prisms included in a light redirecting film 1 according to an embodiment of the invention. As shown in Fig. 2, the light redirecting film 4 comprises an array 6 of parallel triangular prisms wherein one quadrilateral plane of each triangular prism 7 is in the same plane 8. D is the orientation direction of array 6 of parallel triangular prisms. As shown in Fig. 1, the light redirecting film 1 further comprises a primer layer 9 between the reactive adhesive layer 4 and the base layer 3. The primer layer 9 comprises a polyester primer layer or a polyacrylate primer layer. As shown in Fig. 1, the light redirecting film 1 further comprises a light reflecting layer 10, wherein the light reflecting layer covers the plurality of microstructures 5 and conforms to the plurality of microstructures 5. According to a further aspect of the invention, there provides a solar cell module comprising a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet sequentially disposed along a thickness direction of the solar cell module, wherein the solar cell module further includes the above light redirecting film, which is provided between the post encapsulation layer and the back sheet and adheres to a surface of the back sheet through the reactive adhesive layer.
Specifically, Fig. 3 shows a cross-sectional view of a solar cell module 11 according to an embodiment of the invention. The solar cell module 11 comprises a light transmissive element 12, a front encapsulation layer 13, a plurality of solar cells 14 spaced apart from each other, a post encapsulation layer 15, and a back sheet 16 sequentially disposed along a thickness direction T of the solar cell module 11, wherein the solar cell module 11 further includes the above light redirecting film 1, which is provided between the post encapsulation layer 15 and the back sheet 16 and adheres to a surface 17 of the back sheet 16 through the reactive adhesive layer 4.
In this research, the inventors of the present invention found that when the inner layer of the back sheet (i.e., the side facing the solar cells) contains a non-hot melt adhesive material or a fluorine-containing material (for example, a Kpf back sheet manufactured by Saiwu Company or a TFB back sheet manufactured by Zhonglai Company), it is especially prone to create bulges between the back sheet and the light redirecting film under aging conditions. According to the technical solution of the present invention, after a light redirecting film is bonded to a back sheet of a non-hot melt adhesive material or a fluorine-containing material by the adhesive composition according to the present invention and subjected to aging conditions, no bulge is generated between the back sheet and the light redirecting film.
The invention will be described in greater detail with reference to the embodiments. It is to be understood that the description and examples are intended to be illustrative, and not restrictive. The scope of the invention is defined by the appended claims.
Examples
In the present invention, unless otherwise indicated, the reagents employed were all commercially available and used directly without further purification. Further, the mentioned “%” is“% by weight”, and the mentioned“part” is“part by weight”. Tests for Performances
Testing pieces were prepared from the various adhesive compositions prepared in the examples and comparative examples below according to the method for preparing an adhesive layer and a testing piece listed below.
Figure imgf000017_0001
The adhesive compositions prepared in the examples and comparative examples below were extruded respectively at 80-100°C onto a surface of a polyethylene terephthalate film having a thickness of 15 pm using a single-screw extruder manufactured by Kingwell Corporation to form a reactive adhesive film having a thickness of 35 pm.
Figure imgf000017_0002
The light redirecting film having the reactive adhesive film as mentioned above was cut into narrow strips of 5 mm width and 25 cm length. A strip was heat-applied to a side of a Kpf back sheet manufactured by Savigne Company at a speed of 5-10 cm/sec at 100°C. A light-transmitting member (a XYG Model glass manufactured by Shine Separation Co., Ltd.), two EVA encapsulating films (EVA encapsulating films of 9100T and 9210B manufactured by 3M Innovation Co., Ltd.), and the back sheet with a light redirecting film having the reactive adhesive film as prepared above are laminated in a manner that the light redirecting film faced to the EVA encapsulating films to obtain a laminate. The laminate was placed in a KRA-Y1322 laminator manufactured by Qinhuangdao Kezhirui Technology Co., Ltd., and vacuumed at a laminating temperature of 145°C for 5 minutes, then pressurized for 30 seconds and heated for 13 minutes to obtain a testing piece.
The reactive adhesive films and testing pieces obtained as above were tested for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree or the like according to the specific methods listed below.
Moisture-heat aging resistance
The testing pieces obtained above were placed respectively in a Cl 000 environmental testing chamber manufactured by Envirotronics Company, and taken out after being kept at 85°C/85% humidity for 1000 hours. The back sheet side and glass side of the testing pieces were observed by naked eyes to determine if there was bulging, foaming and delamination. If the above phenomenon existed, it is considered that the moisture-heat aging resistance is poor; and if the above phenomenon was not present, the moisture-heat aging resistance is considered to be eligible (Pass).
Exothermic amount
The heat capacity and heat flow of the reactive adhesive films prepared in the examples and comparative examples were directly measured respectively by using a differential scanning calorimeter having a model of Q2000 manufactured by TA Corporation in a temperature range of 20-220 C at a heating rate 10°C/min in nitrogen atmosphere. The exothermic amount (J/g) and the exothermic temperature (°C) were calculated from the obtained DSC curve.
Adhesion
The laminated test pieces were tested respectively for bonding strength (unit: N/cm) between the polymer adhesive layer and the back sheet using an electronic universal testing machine with a model of 5969 manufactured by Instron Company according to ASTM D1876. According to this testing performance, the higher the bonding strength was preferable, and the adhesion performance was superior when the bonding strength is more than 40 N/cm.
Drifting degree
The adhesive compositions prepared in the examples and the comparative examples were respectively extruded on a light redirecting film (T81 Model manufactured by 3M Co.) to obtain a light redirecting film having a reactive adhesive layer having a thickness of 25 pm. The light guiding film was cut into film pieces having a width of 5 mm and a length of 25 cm. A film piece was heat-applied to a textured surface of a XYG Model solar glass produced by Xinyi Glass Company to obtain a solar glass having a light redirecting film. Then, the profile of the light redirecting film on the solar glass was drawn with a marker. Subsequently, a light-transmitting member (an XYG Model glass manufactured by Shine Separation Co., Ltd.), two EVA encapsulating films (EVA encapsulating films of 9100T and 9210B manufactured by 3M Co.), and the solar glass having a light redirecting film as prepared above are laminated to obtain a laminate. The laminate was placed in a KRA-Y1322 laminator manufactured by Qinhuangdao Kezhirui Technology Co., Ltd., and vacuumed at a laminating temperature of 145°C for 5 minutes, then pressurized for 30 seconds and heated for 13 minutes to obtain a testing piece.
Then, the relative distance between the position of the light redirecting film on the laminated testing piece and the profile drawn by the original marker was measured and regarded as a drifting degree (unit: mm). The light redirecting film is considered to be acceptable when the drifting degree is less than 0.5 mm.
The raw materials used in the examples and comparative examples according to the present invention are as shown in Table 1 below. Unless otherwise indicated, the raw materials were used directly without further purification.
Table 1 List of raw materials used in the examples and comparative examples
Figure imgf000019_0001
Example 1
The resin pellets EVA 1, the peroxide crosslinking agent 1, the non-peroxide crosslinking agent 1, the coupling agent 1, the ultraviolet absorber 1 and the ultraviolet stabilizer 2 were mixed and uniformly stirred at room temperature to obtain an adhesive composition 1. In terms of the total weight of the adhesive composition 1, as shown in the following Table 1, the content of the resin pellets EVA 1 was 95.2% by weight, the content of the peroxide crosslinking agent 1 was 1.4% by weight, the content of the non-peroxide crosslinking agent 1 was 0.4% by weight, the content of the coupling agent 1 was 1% by weight, the content of the ultraviolet absorber 1 was 1% by weight, and the content of the ultraviolet stabilizer 2 was 1% by weight.
A reactive adhesive film 1 was prepared from the adhesive composition 1 according to the method for producing a reactive adhesive film as described above. A testing piece 1 was prepared from the reactive adhesive film 1 according to the method for preparing a testing piece as described above. The adhesive composition 1, the reactive adhesive film 1 and the testing piece 1 were subjected to the tests for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree according to the specific methods listed above, and the testing results thereof are shown in Table 2.
Examples 2-9 and Comparative Examples 1-6
Examples 2-9 and Comparative Examples 1-6 were carried out in the same manner as shown in Example 1, except that the kinds, presence or absence and content of each component were changed as shown in Table 2 to obtain respective adhesive combinations.
Respective reactive adhesive films were prepared from the adhesive compositions obtained in Examples 2-9 and Comparative Examples 1-6 according to the method for producing a reactive adhesive film as described above. Respective testing pieces were prepared from the respective reactive adhesive films according to the method for preparing a testing piece as described above. The respective adhesive compositions, reactive adhesive films and testing pieces were subjected to the tests for the performances of moisture-heat aging resistance, exothermic amount, adhesion, and drifting degree according to the specific methods listed above, and the testing results thereof are shown in Tables 2 and 3. Table 2 Details for the Compositions in Examples 1-9 and the testing results for performances thereof
Figure imgf000021_0001
Table 3 Details for the Compositions in Comparative Examples 1-6 and the testing results for performances thereof
Figure imgf000022_0001
As can be seen from Tables 2 and 3 above, according to the embodiments of Examples 1-9, when the adhesive composition underwent an exothermic reaction at a temperature of 95°C or more and had an exothermic amount of 2-40 J/g, when the back sheet side and glass side of the testing pieces were observed by naked eyes, there was no phenomenon of bulging, foaming and delamination, and superior moisture-heat aging resistance was be achieved.
Comparative Example 1 was carried out under the similar conditions as Example 1, except that the adhesive composition of Comparative Example 1 comprised no non-peroxide crosslinking agent. As can be seen from Tables 2 and 3 above, when the adhesive composition of
Comparative Example 1 comprised no non-peroxide crosslinking agent, a low molecular weight product resulting from the coupling of peroxyalkyl radicals and polymer radicals may be present in the adhesive composition system, thereby the bonding strength of the polymer adhesive film was significantly lowered, and the phenomenon of bulging, foaming, and delamination of the light guiding film were observed.
In Comparative Example 2, the adhesive composition system comprised no peroxide crosslinking agent and no non-peroxide crosslinking agent. Thus, the adhesive composition did not undergo an exothermic reaction at a temperature of 95°C or more and released no heat.
Therefore, the reactive adhesive film did not undergo further crosslinking reaction, resulting in bulges in the light redirecting film and the bonding strength thereof was reduced.
In Comparative Example 3, the amount of the non-peroxide crosslinking agent present in the adhesive composition system was too small (only 0.2% by weight), resulting in an exothermic amount of only 1.8 J/g. Thus, the adhesive film did not sufficiently undergo further crosslinking reaction, resulting in some bulges in the light redirecting film and the bonding strength thereof was reduced.
In Comparative Example 4, the amount of the non-peroxide crosslinking agent present in the adhesive composition system was excessive (1.8% by weight), resulting in an excessive exothermic amount of 46 J/g. The excessive exothermic amount caused the shrinkage of the adhesive film to become high and partial wrinkles were generated during application, which was disadvantageous to the appearance of the module and bulges also appeared in the wrinkle portions.
The adhesive composition system of Comparative Example 5 comprised a resin base material of EVA2. As shown in Table 1, the melt flow index (MFI) of the resin base material of EVA2 was larger (that is, 40). The results thereof showed that, although the bonding strength is high, the light redirecting film on the testing piece exhibited a very significant drift (that is, a drift degree greater than 1 mm) and poor moisture-heat aging resistance wherein bulges were formed in the light redirecting film.
The adhesive composition system of Comparative Example 6 comprised a resin base material of EVA3. As shown in Table 1, the VA content of the resin base material of EVA3 was smaller (only 20% by weight). As a result, the bonding strength was lowered, and the phenomenon of bulging, foaming, and delamination was observed.
Obviously, various modifications and variations may be made to this disclosure by the person skilled in the art without deviating from the spirit and the scope of this disclosure. Thus, if these modifications and variations of this disclosure are within the scope of the claims of this invention and equivalent techniques thereof, this disclosure also intends to encompass these modifications and variations.

Claims

WHAT IS CLAIMED IS:
1. An adhesive composition comprising a resin base material, a peroxide crosslinking agent, a non-peroxide crosslinking agent, a coupling agent, an ultraviolet absorber, and an ultraviolet stabilizer, wherein the adhesive composition undergoes an exothermic reaction at a temperature of 95°C or more and has an exothermic amount of 2-40 J/g.
2. The adhesive composition according to claim 1 comprising, in terms of the total weight of the adhesive composition,
90-98wt% of the resin base material;
0.4-1.4wt% of the peroxide crosslinking agent;
0.4-1 6wt% of the non-peroxide crosslinking agent;
0.5-1.5wt% of the coupling agent;
0.5-4wt% of the ultraviolet absorber; and
0.2-2wt% of the ultraviolet stabilizer.
3. The adhesive composition according to claim 1 or 2, wherein the resin base material is one or more selected from a group consisting of an ethylene-vinyl acetate (EVA) copolymer, a polyolefin (PO) resin, polypropylene oxide (PP), polyvinyl butyral (PVB), a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) copolymer, an
ethyl ene-tetrafluoroethylene (ETFE) copolymer, polyvinylidene fluoride (PVDF), polyurethane (PEI), polymethylmethacrylate (PMMA) and polyimide (PI).
4. The adhesive composition according to claim 1 or 2, wherein the resin base material has a melt flow index (MFI) in a range of 10-30.
5. The adhesive composition according to claim 3, wherein the resin base material is an ethylene- vinyl acetate (EVA) copolymer.
6. The adhesive composition according to claim 5, wherein in terms of the total weight of the ethylene-vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 24-30 wt%.
7. The adhesive composition according to claim 5, wherein in terms of the total weight of the ethylene-vinyl acetate (EVA) copolymer, a content of repeating units derived from vinyl acetate in the ethylene-vinyl acetate (EVA) copolymer is in a range of 26-28 wt%.
8. The adhesive composition according to claim 1 or 2, wherein the peroxide crosslinking agent is one or more selected from a group consisting of benzoyl peroxide (BPO), dicumyl peroxide (DCP), t-amyl peroxyacetate (TAP A), tert-butyl peroxy-2-ethylhexyl carbonate (TBEC), and tert-butyl peroxy-3, 5, 5-trimethyl hexanoate (TBPMH).
9. The adhesive composition according to claim 1 or 2, wherein the non-peroxide crosslinking agent is one or more selected from a group consisting of trimethylolpropane triacrylate (TMPTA) and triallyl isocyanurate (TAIC).
10. The adhesive composition according to claim 1 or 2, wherein the coupling agent is one or more selected from a group consisting of a silane coupling agent and a phthalic ester coupling agent.
11. The adhesive composition according to claim 1 or 2, wherein the ultraviolet absorber is one or more selected from a group consisting of a salicyl ester ultraviolet absorber, a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber.
12. The adhesive composition according to claim 11, wherein the salicyl ester ultraviolet absorber is one or more selected from a group consisting of methyl salicylate, ethyl salicylate and octyl salicylate.
13. The adhesive composition according to claim 11, wherein the benzophenone ultraviolet absorber is one or more selected from a group consisting of
2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-n-octyloxybenzophenone.
14. The adhesive composition according to claim 11, wherein the benzotriazole ultraviolet absorber is one or more selected from a group consisting of
2-(2’ -hydroxy-3’, 5’-di-tert-phenyl)-5-chlorobenzotriazole and 2-(2’ -hydroxy-5’-methylphenyl) benzotriazole.
15. The adhesive composition according to claim 1 or 2, wherein the ultraviolet stabilizer is a hindered amine ultraviolet stabilizer.
16. The adhesive composition according to claim 15, wherein the hindered amine ultraviolet stabilizer is one or more selected from a group consisting of polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl- 1 -piperidineethanol) ester,
poly[(6-morpholinyl-5-triazine-2,4-diyl) (2,2,6,6-tetramethylpiperidinyl)imino
hexamethylene[(2,2,6,6-tetramethylpiperidyl)-imino]],
4-benzoyloxy-2,2,6,6-tetramethylpiperidine and tris(l,2,2,6,6-pentapiperidinyl) phosphite.
17. A light redirecting film, comprising a light redirecting layer, a base layer and a reactive adhesive layer in turn, wherein the reactive adhesive layer comprises the adhesive composition according to claim 1.
18. The light redirecting film according to claim 17, wherein the base layer has been subjected to a physical surface treatment.
19. The light redirecting film according to claim 18, wherein the physical surface treatment is corona treatment or plasma treatment.
20. The light redirecting film according to claim 17, wherein the reactive adhesive layer has a thickness in a range of 10-100 pm.
21. The light redirecting film according to claim 17, wherein the light redirecting layer comprises a plurality of microstructures that are orderly arranged and protruded from the base layer.
22. The light redirecting film according to claim 17, wherein the light redirecting layer comprises a plurality of microstructures that are randomly arranged and protruded from the base layer.
23. The light redirecting film according to claim 21 or 22, wherein the plurality of microstructures comprises an array of abutting triangular prisms whose orientation direction is non-linearly oriented.
24. The light redirecting film according to claim 21 or 22, wherein the plurality of microstructures comprises an array of parallel triangular prisms wherein one quadrilateral plane of each triangular prism is in the same plane.
25. The light redirecting film according to claim 17, wherein the light redirecting film further comprises a primer layer between the reactive adhesive layer and the base layer.
26. The light redirecting film according to claim 25, wherein the primer layer is a polyester primer layer or a polyacrylate primer layer.
27. The light redirecting film according to claim 21 or 22, wherein the light redirecting film further comprises a light reflecting layer, wherein the light reflecting layer covers the plurality of microstructures and conforms to the plurality of microstructures.
28. A solar cell module comprising a light transmissive element, a front encapsulation layer, a plurality of solar cells spaced apart from each other, a post encapsulation layer, and a back sheet sequentially disposed along a thickness direction of the solar cell module, wherein the solar cell module further includes the light redirecting film according to claim 17, which is provided between the post encapsulation layer and the back sheet and adheres to a surface of the back sheet through the reactive adhesive layer.
29. The solar cell module according to claim 28, wherein a side of the back sheet facing the solar cells comprises a non-hot melt adhesive material.
30. The solar cell module according to claim 28, wherein a side of the back sheet facing the solar cells comprises a fluorine-containing material.
PCT/IB2019/060126 2018-11-30 2019-11-25 Adhesive composition, light redirecting film and solar cell module WO2020109968A1 (en)

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