Multilayer structure having adhesive properties

Abstract

The present invention relates to a multilayer structure comprising an adhesive layer and a carrier film-forming layer in direct contact therewith wherein the adhesive layer comprises a polyolefin A and a functional polyolefin and has a melting temperature of 80 DEG C to 120 DEG C, and wherein the carrier film comprises a polyamide graft polymer and has a flow temperature greater than 160 DEG C. The invention further relates to a method for producing a multilayer structure, to the use of such a multilayer structure for producing photovoltaic modules, to a method for producing such modules, and to the photovoltaic modules themselves.

Description

Field of the Invention

[0001] The present invention relates to a multi-layer structure, in particular a two-layer structure, which can be particularly used as an encapsulant for a photovoltaic module. The present invention also relates to a photovoltaic module including such a multi-layer structure. Background Art

[0002] Global warming associated with greenhouse gases released by fossil fuels has further stimulated the interest in alternative energy solutions that do not emit such gases during their operation, such as photovoltaic modules.

[0003] There are many types of photovoltaic module structures.

[0004] Figure 1 A conventional photovoltaic cell is shown; the photovoltaic cell (10) includes unit cells (12), and the unit cells contain a photovoltaic sensor (14) in contact with electronic collectors (16) located above (upper collector) and below (lower collector) the photovoltaic sensor. The upper collector (16) of the unit cell is connected to the lower collector (16) of another unit cell (12) via a conductive strip (18), and the conductive strip (18), also called an electrical interconnector, is usually made of a metal alloy. In other embodiments, all the interconnectors are located on the same side of the unit cell. All these unit cells (12) are connected in series and / or in parallel together to form a photovoltaic cell (10). When the photovoltaic cell (10) is placed under a light source, it delivers a direct current that can be collected at the ends (19) of the cell (10).

[0005] Figure 2 A photovoltaic module (20) is represented, which includes a photovoltaic cell (10) encapsulated in an encapsulant (22) composed of an upper part and a lower part. Figure 1 The encapsulated cell is also protected by an upper protective layer (24) (also called a front plate) and a protective layer on the back of the module (also called a backsheet) (26). The upper protective layer (24), usually made of glass, provides shock and moisture protection for the photovoltaic cell. The protective layer on the back of the module (26), usually made of a thermoplastic or crosslinkable resin, also helps with moisture protection, and in addition, helps with the electrical insulation of the unit cell by avoiding any contact with the external environment.

[0006] To ensure effective protection, it is important that the encapsulant perfectly fills the space between the photovoltaic cell and the protective layer. In addition, its adhesion to the protective layer must be perfect and durable even at temperatures of 80 °C or higher that can be reached under solar radiation.

[0007] To promote adhesion, "chemical" techniques can be used by providing specific adhesives or adhesion promoters, or physical techniques such as surface treatment by corona or plasma effects. However, these methods require additional operations that are sometimes complex for the usually disappointing results and result in non-negligible costs. In addition, physical surface treatment is unstable over time and requires storage and handling precautions.

[0008] Currently, to manufacture a photovoltaic module, a "front plate", an encapsulant, cells, and a "back plate" are usually assembled simultaneously by a vacuum lamination process. The encapsulant is melted during the lamination step to coat the active layer of the cells.

[0009] In addition to handling many films, this assembly method by lamination has the drawback associated with the shrinkage of the encapsulant film, which can be up to 10%, and sometimes even 50%. This shrinkage can cause defects in the photovoltaic module, such as bubbles, wrinkles, blisters, defects of overlapping on the edges, or breaks in the connectors between the unit cells. All these defects result in waste or can reduce the lifespan and efficiency of the photovoltaic module.

[0010] To limit these problems, the encapsulant film can be produced by an extrusion process followed by a post-annealing step, but this reduces the extrusion speed and thus increases its cost.

[0011] Patent application EP 2 673 809 A1 discloses a double-layer film composed of a back plate and an encapsulant, such that at least some of these problems can be overcome. However, the implementation of these two-layer structures requires sequentially stacking the first layer of encapsulant, the photovoltaic module, the second layer of encapsulant, and the layer that finally forms the back plate, as Figure 2 shown. In addition to the 400 μm thick first sealant, two-layer structures with a thickness of 800 μm are also described. The large thickness of these structures significantly increases the weight and cost. In addition, the encapsulant does not provide sufficient adhesion to the metal used in the process of the prior lamination step on the surface of the metal interconnector.

[0012] In addition, these double-layer films cannot be used to prepare photovoltaic modules with certain geometries, especially the connections located on the same side as the photovoltaic sensors, such as those described in patent application WO 2004 / 021455, and which require directly laminating the encapsulant onto the surface of the interconnector.

[0013] Therefore, there is a need for multi-layer structures, especially for photovoltaic modules, which can overcome the disadvantages of the prior art, especially improving the productivity of the manufacturing process and the quality of the photovoltaic module, and which are universal and thus compatible with different geometric configurations of the assembly methods for photovoltaic modules. Summary of the Invention

[0014] The object of the present invention is to remedy the problems encountered in the prior art by proposing a multilayer structure, in particular a two-layer structure, comprising an adhesive layer and a carrier film.

[0015] In its broadest definition, the present invention relates to a multilayer structure comprising an adhesive layer that can be used as an encapsulant and a carrier film that can be used as a backsheet, characterized in that the adhesive layer comprises polyolefin A and a functional polyolefin and has a specific melting point, since the carrier film has a specific flow temperature.

[0016] Specifically, it has been found that by combining polyolefin A with a functional polyolefin in the adhesive layer, a multilayer structure can be obtained that has both very good thermal stability and excellent adhesion to the metal of the electrical interconnectors of photovoltaic cells.

[0017] Better adhesion of the multilayer structure to the interconnector has a twofold advantage. First, it can facilitate the assembly method, in particular by avoiding prior surface treatment. Second, it can ensure a reliable electrical contact between the interconnector and the photovoltaic cell, thus giving the photovoltaic module better efficiency and a longer lifespan.

[0018] Finally, the multilayer structure of the present invention can have a small thickness, in particular less than 100 μm.

[0019] Thus, the multilayer structure according to the present invention allows for the manufacture of photovoltaic modules of better quality and lower cost.

[0020] Thus, the present invention relates to a multilayer structure comprising an adhesive layer and a layer forming a carrier film in direct contact therewith, wherein:

[0021] (a) the adhesive layer comprises:

[0022] - polyolefin A, selected from homopolymers of ethylene and copolymers of ethylene with α-olefins, copolymers of ethylene with vinyl esters of carboxylic acids (in particular ethylene vinyl acetate (EVA)) or (co)polymers comprising units of (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid sec-butyl ester, (meth)acrylic acid isobutyl ester or (meth)acrylic acid tert-butyl ester; and

[0023] - a functional polyolefin different from polyolefin A, comprising a polyolefin backbone containing residues of at least one unsaturated monomer (Y), the residues of the unsaturated monomer (Y) being fixed to the backbone by grafting or copolymerization;

[0024] the melting temperature of the adhesive layer is between 80 °C and 120 °C,

[0025] b) the carrier film comprises a polyamide graft polymer, the polyamide graft polymer comprising:

[0026] - The polyolefin main chain (50% to 95% by mass of the polyamide graft polymer) contains residues of at least one unsaturated monomer (X) and at least one polyamide graft (5% to 50% by mass of the polyamide graft polymer), wherein:

[0027] o The polyamide graft is connected to the polyolefin main chain through residues of the unsaturated monomer (X), and the residues of the unsaturated monomer (X) contain functional groups capable of reacting with a polyamide having at least one amine end and / or at least one carboxylic acid end through a condensation reaction.

[0028] o The residues of the unsaturated monomer (X) are fixed to the main chain by grafting or copolymerization.

[0029] o The polyolefin main chain and the polyamide graft are selected such that the polyamide graft polymer has a flow temperature greater than 160 °C measured by DSC according to ISO 11357-1:2016, ISO 11357-2:2020, ISO 11357-3:2018, and the flow temperature is defined as the highest temperature among the melting temperature and the glass transition temperature of the polyamide graft and the polyolefin main chain.

[0030] Other advantageous features of the present invention are as follows:

[0031] - The melting temperature of the adhesive layer is between 90 °C and 110 °C.

[0032] - The adhesive layer has a melt flow index (MFI) of 0.2 - 10 g / 10 min, preferably 0.4 - 3 g / 10 min, particularly 0.6 - 2 g / 10 min measured at 190 °C under 2.16 kg according to ASTM standard D 1238.

[0033] - The adhesive layer comprises:

[0034] ο 65% to 95% by weight of polyolefin A;

[0035] ο 5% to 35% by weight of functional polyolefin; and

[0036] ο 0 to 5% by weight of one or more additives.

[0037] - The thickness of the adhesive layer is 20 - 60 μm.

[0038] - The thickness of the carrier film is 5 - 40 μm.

[0039] - The α-olefin comonomer of polyolefin A in the adhesive layer is selected from ethylene-propylene, ethylene-butene, and ethylene-octene.

[0040] - The functional polyolefin of the adhesive layer is a polyolefin containing residues of at least one unsaturated monomer (Y), and the unsaturated monomer (Y) is maleic anhydride.

[0041] - As measured according to ASTM standard D 1238 at 230 °C under 2.16 kg, the melt flow index (MFI) of the carrier film is 0.2 - 10 g / 10min, preferably 0.4 - 3 g / 10min, especially 0.6 - 2 g / 10min.

[0042] - The carrier film bears the adhesive layer on one of its surfaces.

[0043] - The carrier film bears the adhesive layer on both of its surfaces.

[0044] - The carrier film is assembled to the adhesive layer by co - extrusion.

[0045] According to another aspect, the present invention relates to the use of such a multilayer structure for manufacturing a photovoltaic module.

[0046] According to yet another aspect, the present invention relates to a method for preparing a photovoltaic module, in which a photovoltaic cell is encapsulated with such a multilayer structure.

[0047] In this method, the encapsulation may include the following steps:

[0048] (i) Fixing conductive wires to the surface of the adhesive layer of such a multilayer structure at a temperature below the melting temperature of the adhesive layer to form an assembly;

[0049] (ii) Contacting the assembly with a photovoltaic cell at a temperature between the melting temperature of the adhesive layer and the flow temperature of the carrier film.

[0050] Finally, according to the last aspect, the present invention relates to a photovoltaic module including such a multilayer structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] With reference to the accompanying drawings, the following description is given by way of illustration only and not in a limiting sense, in which:

[0052] - Figure 1 Shows an example of a photovoltaic cell, parts (a) and (b) are three - quarter views, part (a) shows the unit cell before connection, part (b) shows the view after connecting two unit cells; part (c) is a top view of the complete photovoltaic cell; and

[0053] - Figure 2 Shows a cross - section of a photovoltaic module, in which its "conventional" photovoltaic sensor is encapsulated by an upper encapsulant film and a lower encapsulant film. DETAILED DESCRIPTION

[0054] Thus, according to a first aspect, the present invention relates to a multi-layer structure, in particular as an encapsulant for a photovoltaic cell, which comprises an adhesive layer and a layer forming a carrier film in direct contact therewith, wherein the adhesive layer comprises polyolefin A and a functionalized polyolefin, the melting temperature of the adhesive layer is from 80 °C to 120 °C, and wherein the carrier film comprises a specific polyamide graft polymer having a flow temperature greater than 160 °C, the flow temperature being measured by DSC according to ISO 11357-1:2016, ISO 11357-2:2020, ISO 11357-3:2018, and the flow temperature being defined as the highest temperature among the melting temperature and the glass transition temperature of the polyamide graft and the polyolefin backbone.

[0055] A. Multi-layer structure

[0056] According to the invention, the adhesive layer of the multi-layer structure is in direct contact with the carrier film.

[0057] In the absence of additional layers, the multi-layer structure can form a bilayer structure. However, it can also include other layers, in principle any layer. According to a preferred embodiment, the multi-layer structure can be a three-layer structure and can in particular comprise a carrier film provided with adhesive layers as defined below on its two faces.

[0058] A.1. Adhesive layer

[0059] According to the invention, the adhesive layer of the multi-layer structure comprises a specific polyolefin A and a different functional polyolefin, and the melting temperature of the adhesive layer is from 80 °C to 120 °C. The polyolefin will be described in more detail below.

[0060] Polyolefin A

[0061] The polyolefin A present in the adhesive layer can be a homopolymer of ethylene or a copolymer of ethylene with a comonomer selected from α-olefins, (meth)acrylic acid alkyl esters or vinyl esters of carboxylic acids (especially vinyl acetate). In the copolymer, the α-olefin can include 3 to 30 and in particular 3 to 8 carbon atoms. Examples of α-olefins that can be mentioned include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene, 1-tetracosene, 1-hexacosene, 1-octacosene and 1-triacontene. These α-olefins can be used alone or as a mixture of two or more.

[0062] Preferably, the ethylene-α-olefin copolymer contains a ethylene mass content of greater than 50%.

[0063] The ethylene-α-olefin copolymer is obtained by methods known to those skilled in the art, such as Ziegler-Natta, metallocene or organometallic polymerization as described, for example, in WO 2008 / 036 707.

[0064] Particularly preferred as polyolefin A is polyethylene, especially linear low density (LLDPE) polyethylene, or a copolymer of ethylene with a single α-olefin selected from ethylene-propylene, ethylene-butene and ethylene-octene.

[0065] According to another embodiment, polyolefin A is a copolymer of ethylene and an alkyl (meth)acrylate, the term "alkyl (meth)acrylate" including alkyl acrylate or alkyl methacrylate. The alkyl chain of these (meth)acrylates may contain up to 30 carbon atoms. Mention may be made of alkyl chains including methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl and nonacosyl. Methyl, ethyl and butyl (meth)acrylates are preferred.

[0066] Ethylene-alkyl (meth)acrylate copolymers are generally obtained by methods known to those skilled in the art, such as autoclave or tubular high-pressure methods.

[0067] According to a particularly preferred embodiment, polyolefin A is a copolymer of ethylene and vinyl acetate (EVA).

[0068] Preferably, the melting temperature of polyolefin A is between 90 °C and 110 °C, especially between 90 °C and 105 °C.

[0069] According to one embodiment, the melting enthalpy of polyolefin A is less than 130 J / g, and especially between 80 and 120 J / g (second heating by DSC at 40 °C / min according to ISO 11347).

[0070] The density of polyolefin A measured according to ASTM standard D 1505 is preferably from 0.860 to 0.960, especially from 0.860 to 0.920.

[0071] Specifically, without wishing to limit itself to a particular theory, the applicant has been able to observe that the low melting enthalpy in the above range, which reflects low crystallinity, makes it possible to advantageously influence the adhesion of the adhesive layer to the metal.

[0072] Functional polyolefin

[0073] For the purposes of this specification, the term "functional polyolefin" means a polyolefin different from polyolefin A present in the adhesive layer, which contains reactive functional groups and is capable of reacting upon contact with a metal surface.

[0074] Such reactive functional groups are in particular epoxy, carboxylic acid, carboxylic anhydride, carboxamide and carboxylic ester functional groups.

[0075] The functional polyolefin present in the adhesive layer contains a polyolefin backbone which contains residues of at least one unsaturated monomer (Y) selected from unsaturated epoxides, unsaturated carboxylic anhydrides, unsaturated carboxylic acids or their salts, and the residues of the unsaturated monomer (Y) are fixed to the backbone by grafting or copolymerization.

[0076] These functions promote the interaction with the metal surface in contact with the electrical interconnector, which improves the adhesion between the multilayer structure and the electrical interconnector.

[0077] The functional polyolefin can in particular be derived from monomers such as methyl (meth)acrylate, (meth)acrylamide or vinyl acetate.

[0078] According to one embodiment, the polyolefin backbone of the functional polyolefin is a polyethylene backbone, in particular a homopolymer or copolymer of ethylene.

[0079] The unsaturated monomer (Y) can be an unsaturated epoxide, which is in particular selected from aliphatic glycidyl esters and ethers such as allyl glycidyl ether, vinyl glycidyl ether, maleic acid glycidyl ester and itaconic acid glycidyl ester, glycidyl acrylate and glycidyl methacrylate; cycloaliphatic glycidyl esters and ethers, such as 2-cyclohexene-1-glycidyl ether, cyclohexene-4,5-diglycidyl carboxylate, cyclohexene-4-glycidyl carboxylate, 5-norbornene-2-methyl-2-glycidyl carboxylate and endo-cis-bicyclo(2,2,1)-5-heptene-2,3-diglycidyl dicarboxylate, and glycidyl methacrylate is preferred.

[0080] As a variant, the unsaturated monomer (Y) can be an unsaturated carboxylic acid or its salt, in particular acrylic acid or methacrylic acid and their salts.

[0081] As a variant, the unsaturated monomer (Y) can be an unsaturated carboxylic acid ester, in particular an alkyl (meth)acrylate, the term "alkyl (meth)acrylate" including alkyl acrylates or alkyl methacrylates. The alkyl chains of these (meth)acrylates can contain up to 30 and in particular up to 24 carbon atoms. Mention may be made of alkyl chains including methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl and nonacosyl, in particular methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.

[0082] As a variant, the unsaturated monomer (Y) can be a carboxylic anhydride, in particular selected from maleic anhydride, itaconic anhydride, citraconic anhydride, allyl succinic anhydride, cyclohex-4-ene-1,2-dicarboxylic anhydride, 4-methylene cyclohex-4-ene-1,2-dicarboxylic anhydride, bicyclo(2,2,1)hept-5-ene-2,3-dicarboxylic anhydride and x-methyl bicyclo(2,2,1)hept-5-ene-2,2-dicarboxylic anhydride. Among them, maleic anhydride is preferred.

[0083] The unsaturated monomer (Y) can also be a vinyl ester of a carboxylic acid, in particular vinyl acetate.

[0084] As a variant, the unsaturated monomer (Y) can also be a (meth)acrylamide selected from acrylamide and methacrylamide.

[0085] The unsaturated monomer (Y) in the functional polyolefin is fixed by grafting or copolymerization.

[0086] Preferably, the functional polyolefin does not contain any polyamide grafting.

[0087] Preferably, the functional polyolefin is an ethylene copolymer containing residues of an unsaturated carboxylic anhydride, in particular maleic anhydride.

[0088] The ethylene copolymer can be a copolymer of ethylene and a comonomer selected from esters of unsaturated carboxylic acids, such as alkyl acrylates or alkyl methacrylates grouped under the term "alkyl (meth)acrylate" as specified above.

[0089] The copolymer of ethylene and an unsaturated carboxylic acid ester can be obtained by methods known to those skilled in the art, such as autoclave or tubular high-pressure methods.

[0090] In a preferred embodiment, the functional polyolefin is an ethylene-(alkyl (meth)acrylate)-maleic anhydride terpolymer.

[0091] According to one embodiment, the adhesive layer comprises at least 65% by weight of polyolefin A as defined above.

[0092] According to another embodiment, the adhesive layer comprises at least 5% by weight of a functional polyolefin.

[0093] According to a preferred embodiment, the adhesive layer comprises:

[0094] - 65% to 95% by weight of polyolefin A as defined above,

[0095] - 5% to 30% by weight of a functional polyolefin; and

[0096] - 0% to 5% by weight of additives, which are particularly selected from plasticizers, adhesion promoters, UV stabilizers, UV absorbers, antioxidants and pigments.

[0097] A plasticizer can be added to the adhesive layer in order to facilitate implementation and improve the productivity of the method for manufacturing the multilayer structure and / or the photovoltaic module. Examples that may be mentioned include naphthalene or aromatic paraffin mineral oil, which can also improve the adhesion of the structure according to the invention. As plasticizers, phthalates, azelates, adipates or tricresyl phosphate can also be mentioned.

[0098] A colorant compound or a brightening compound can also be added.

[0099] Similarly, although not essential, an adhesion promoter can be advantageously added in order to further improve the adhesiveness of the structure. The adhesion promoter is a non-polymeric component; it can be organic, crystalline or inorganic, and more preferably semi-inorganic semi-organic. Among them, silanes or titanates can be mentioned, such as monoalkyl titanates, trichlorosilanes and trialkoxysilanes. Advantageously, trialkoxysilanes containing epoxy groups, vinyl groups or amine groups will be used, especially when these adhesion promoters are added in the form of a masterbatch. These adhesion promoters can also be mixed or diluted with the functional or non-functional polyolefins of the adhesive layer by techniques known to those skilled in the art (such as compounding).

[0100] Since UV radiation can cause slight yellowing of the adhesive layer, UV stabilizers and UV absorbers (such as benzotriazoles, benzophenones and other hindered amines) can be added to the adhesive layer and / or the carrier film to extend the transparency of the multilayer structure and thus its lifespan.

[0101] In addition, relative to the total weight of the composition, the adhesive layer can contain 0 to 5% by weight, especially 0.1% to 4.5% by weight, especially 0.5% to 4% by weight and most especially 1% to 3% by weight of one or more of these additives.

[0102] In addition, the adhesive layer may contain one or more antioxidants to limit yellowing during the manufacture of the adhesive layer. Preferred antioxidants are, for example, phosphorus-containing compounds (phosphonites and / or phosphites) and hindered phenols.

[0103] Relative to the total weight of the composition, the adhesive layer may in particular contain from 0 to 3% by weight, in particular from 0.1% by weight to 2.5% by weight, particularly from 0.5% by weight to 2% by weight and most particularly from 1% by weight to 1.5% by weight of one or more antioxidants.

[0104] Pigments, such as colorant compounds or brightening compounds, may also be added to the adhesive layer, and their proportion is generally from 0.01% to 2% relative to the total mass of the composition.

[0105] According to one embodiment, the thickness of the adhesive layer is between 20 and 60 μm.

[0106] The melting temperature of the adhesive layer is preferably between 80 °C and 110 °C, preferably between 90 °C and 100 °C.

[0107] Specifically, the inventors have observed that if the melting temperature is low, the multi-layer structure may be difficult to process, especially during the co-extrusion step with the carrier film and / or during its subsequent use, especially during the lamination step on the wire surface. On the contrary, a melting temperature above 120 °C is generally accompanied by a higher crystallinity, which can reduce the adhesion to the wire.

[0108] According to one embodiment, the adhesive layer has a melt flow index (MFI) or heat flow index between 0.2 g / 10min and 10 g / 10min, preferably between 0.4 g / 10min and 3 g / 10min, and more preferably between 0.6 g / 10min and 2 g / 10min.

[0109] A.2. Carrier film

[0110] The carrier film comprises a polyamide-grafted polymer, the polyamide-grafted polymer comprising a polyolefin backbone and at least one polyamide graft, the polyolefin backbone containing residues of at least one unsaturated monomer (X), the polyamide graft being attached to the polyolefin backbone through the residues of the unsaturated monomer (X), the unsaturated monomer (X) comprising a functional group capable of reacting with polyamide by a condensation reaction, the polyolefin backbone and the polyamide graft being selected such that the flow temperature of the polyamide-grafted polymer is greater than 160 °C.

[0111] The flow temperature of the polyamide graft polymer is defined as the highest temperature among the melting temperature and the glass transition temperature of the polyamide graft and the polyolefin backbone. The backbone and the graft are selected such that the flow temperature of the polyamide graft polymer is greater than 160 °C.

[0112] The polyamide graft polymer comprises 50% to 95% by weight, preferably 60% to 90% by weight and especially 70% to 85% by weight of a polyolefin backbone containing residues of at least one unsaturated monomer (X).

[0113] Regarding the polyolefin backbone, it is preferably a polymer containing an α-olefin as a monomer, and the α-olefin especially includes 2 to 30 carbon atoms.

[0114] Examples of α-olefins that may be mentioned include ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene, 1-tetracosene, 1-hexacosene, 1-octacosene and 1-triacontene.

[0115] Cycloolefins containing 3 to 30 and especially 3 to 20 carbon atoms may also be mentioned, such as cyclopentane, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene, and 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene; dienes and polyenes, such as butadiene, isoprene, 4-methyl-1,3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, 1,3-hexadiene, 1,3-octadiene, 1,4-octadiene, 1,5-octadiene, 1,6-octadiene, ethylidene norbornene, vinyl norbornene, dicyclopentadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene and 5,9-dimethyl-1,4,8-decatriene; vinyl aromatic compounds such as mono- or poly-alkylstyrenes (including styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene and p-ethylstyrene), and derivatives containing functional groups such as methoxystyrene, ethoxystyrene, vinyl benzoic acid, methyl vinyl benzoate, benzyl vinyl acetate, hydroxystyrene, o-chlorostyrene, p-chlorostyrene, divinylbenzene, 3-phenylpropene, 4-phenylpropene, α-methylstyrene, vinyl chloride, 1,2-difluoroethylene, 1,2-dichloroethylene, tetrafluoroethylene and 3,3,3-trifluoro-1-propene, preferably propylene and ethylene.

[0116] The polyolefin can be a homopolymer when only one α-olefin is polymerized. Examples that can be mentioned are polyethylene (PE) or polypropylene (PP). It can also be a copolymer when at least two comonomers are copolymerized in the polymer chain, the first of the at least two monomers being an α-olefin and the other comonomers being monomers capable of polymerizing with the first monomer.

[0117] Other comonomers that can be mentioned include:

[0118] - One of the α-olefins already mentioned above, which is different from the first α-olefin comonomer;

[0119] - Dienes, such as 1,4-hexadiene, ethylidene, norbornene or butadiene;

[0120] - Esters of unsaturated carboxylic acids, such as alkyl acrylates or alkyl methacrylates grouped under the term "(meth)acrylic acid alkyl ester". The alkyl chains of these (meth)acrylates can contain up to 30 carbon atoms. Alkyl chains that can be mentioned include methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl and nonacosyl, preferably methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate; and

[0121] - Vinyl esters of carboxylic acids. As examples of vinyl esters of carboxylic acids, vinyl acetate, vinyl versatate, vinyl propionate, vinyl butyrate or vinyl maleate can be mentioned, preferably vinyl acetate.

[0122] Advantageously, the polyolefin backbone consists of at least 50 mol% of the first comonomer.

[0123] The preferred polyolefin backbone consists of an ethylene / (meth)acrylic acid alkyl ester copolymer. By using this polyolefin backbone, excellent resistance to photo and thermal aging is obtained.

[0124] According to the present invention, the polyolefin backbone contains at least one residue of an unsaturated monomer (X) that is capable of reacting with the acid and / or amine functional groups grafted to the polyamide by a condensation reaction. It should be noted that this unsaturated monomer (X) is not the "second comonomer".

[0125] As the unsaturated monomer (X), the following can be mentioned:

[0126] - Unsaturated epoxides, these include aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate and glycidyl itaconate, glycidyl acrylate and glycidyl methacrylate; alicyclic glycidyl esters and ethers, such as 2 - cyclohexene - 1 - glycidyl ether, cyclohexene - 4,5 - diglycidyl carboxylate, cyclohexene - 4 - glycidyl carboxylate, 5 - norbornene - 2 - methyl - 2 - glycidyl carboxylate and endo - cis - bicyclo(2,2,1) - 5 - heptene - 2,3 - diglycidyl dicarboxylate, glycidyl methacrylate is preferred.

[0127] - Unsaturated carboxylic acids and their salts, such as acrylic acid or methacrylic acid and their salts.

[0128] - Carboxylic anhydrides, which are for example selected from maleic anhydride, itaconic anhydride, citraconic anhydride, allyl succinic anhydride, cyclo - 4 - ene - 1,2 - dicarboxylic anhydride, 4 - methylenecyclo - 4 - ene - 1,2 - dicarboxylic anhydride, bicyclo(2,2,1)hept - 5 - ene - 2,3 - dicarboxylic anhydride and x - methylbicyclo(2,2,1)hept - 5 - ene - 2,2 - dicarboxylic anhydride, especially maleic anhydride.

[0129] The unsaturated monomer (X) is preferably selected from unsaturated carboxylic anhydrides and unsaturated epoxides. In particular, for the condensation of polyamide grafting with the polyolefin backbone, when the reactive end of the polyamide graft is a carboxylic acid functional group, the unsaturated monomer (X) is preferably an unsaturated epoxide. When the reactive end of the polyamide graft is an amine functional group, the unsaturated monomer (X) is advantageously an unsaturated epoxide and preferably an unsaturated carboxylic anhydride.

[0130] According to an advantageous version of the invention, the preferred number of unsaturated monomers (X) fixed on the polyolefin backbone on average is greater than or equal to 1.3 and / or preferably less than or equal to 10.

[0131] Thus, if (X) is maleic anhydride and the number - average molar mass of the polyolefin is 15 000 g / mol, it has been found that this corresponds to an anhydride proportion of at least 0.8 mass% and at most 6.5% of the entire polyolefin backbone. These values related to the mass of the polyamide graft determine the proportion of polyamide and the backbone in the polyamide - grafted polymer.

[0132] The polyolefin backbone containing residues of the unsaturated monomer (X) is obtained by the polymerization of monomers (a first comonomer, an optional second comonomer, and an optional unsaturated monomer (X)). This polymerization can be carried out via a high-pressure free-radical method or a solution method in an autoclave or a tubular reactor, which methods and reactors are well known to those skilled in the art. When the unsaturated monomer (X) is not copolymerized in the polyolefin backbone, it is grafted onto the polyolefin backbone. Grafting is also an operation known per se. If several different functional monomers (X) are copolymerized and / or grafted onto the polyolefin backbone, the composition will be according to the present invention.

[0133] Depending on the type and proportion of the monomers, the polyolefin backbone can be semi-crystalline or amorphous. For amorphous polyolefins, only the glass transition temperature is observed, while for semi-crystalline polyolefins, both the glass transition temperature and the melting temperature are observed. By adjusting the type and proportion of the monomers, a polyolefin backbone with the desired glass transition temperature and melting temperature (if any) can be obtained. The molar mass of the polyolefin backbone can be varied to obtain the desired viscosity.

[0134] The melt flow index (MFI) of the polyolefin backbone is preferably 3 - 400 g / 10 min, especially 10 - 300 g / 10 min, especially 50 - 200 g / 10 min (190 °C, 2.16 kg, ASTM D 1238).

[0135] Preferably, its density as measured according to standard ISO 1183:2019 is advantageously between 0.91 and 0.96.

[0136] The polyamide graft polymer comprises a polyolefin backbone containing residues of at least one unsaturated monomer (X) as described above and at least one polyamide graft attached to the polyolefin backbone via the residues of the unsaturated monomer (X).

[0137] The polyamide graft can be a homopolyamide or a copolyamide. The polyamide graft can in particular be aliphatic, cycloaliphatic or semi-aromatic.

[0138] Among the homopolyamides, preferred are aliphatic polyamides produced by the polycondensation of:

[0139] - lactams,

[0140] - aliphatic α,ω-amino carboxylic acids, or

[0141] - aliphatic diamines and aliphatic diacids.

[0142] As examples of lactams, mention may be made of caprolactam, enantholactam and laurolactam.

[0143] As examples of aliphatic α,ω-amino carboxylic acids, mention may be made of aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid.

[0144] As examples of aliphatic diamines, mention may be made of hexamethylenediamine, dodecamethylenediamine and trimethylhexamethylenediamine.

[0145] As examples of aliphatic diacids, mention may be made of adipic acid, azelaic acid, suberic acid, sebacic acid and dodecanedioic acid.

[0146] In the case of aliphatic homopolyamides, examples that may be mentioned in a non-limiting manner include the following polyamides: polycaprolactam (PA6), polyundecanamide (PA11), polylaurolactam (PA12), polybutylene adipamide (PA4.6), polyhexamethylene adipamide (PA6.6), polyhexamethylene azelamide (PA6.9), polyhexamethylene sebacamide (PA6.10), polyhexamethylene dodecanediamide (PA6.12), polydecamethylene dodecanediamide (PA10.12), polydecamethylene sebacamide (PA10.10) and polydodecamethylene dodecanediamide (PA12.12). PA6 is particularly preferred.

[0147] In the case of alicyclic homopolyamides, mention may in particular be made of those resulting from the condensation of alicyclic diamines and aliphatic diacids.

[0148] Examples of alicyclic diamines that may be mentioned include 4,4'-methylenebis(cyclohexylamine), also known as p-bis(aminocyclohexyl)methane or PACM, and 2,2'-dimethyl-4,4'-methylenebis(cyclohexylamine), also known as bis(3-methyl-4-aminocyclohexyl)methane or BMACM.

[0149] In the case of alicyclic homopolyamides, mention may in particular be made of polyamides PACM.12, BMACM.10 and BMACM.12.

[0150] Semi-aromatic homopolyamides may result from the condensation of:

[0151] - aliphatic diamines and aromatic diacids such as terephthalic acid (T) and isophthalic acid (I). The polyamides obtained are then generally referred to as "polyphthalamides" or PPA;

[0152] - aromatic diamines, such as xylylenediamine, more particularly metaxylylenediamine (MXD) and aliphatic diacids.

[0153] In this family of polyamides, mention may in particular be made of polyamides 6.T, 6.I, MXD.6 and MXD.10.

[0154] As a variant, polyamide grafts are copolyamides. The latter result from the polycondensation of at least two of the above monomers for obtaining homopolyamides.

[0155] The term "monomer" in the context of this specification of copolyamides shall be considered to mean "repeating unit". In particular, it is special when the repeating unit of PA consists of a combination of a diacid and a diamine. It is considered as a combination of a diamine and a diacid, i.e., a diamine:diacid pair (in equimolar amounts), which corresponds to the monomer. This is explained by the fact that individually, a diacid or a diamine is only a structural unit and is not sufficient by itself to polymerize to obtain a polyamide.

[0156] Thus, copolyamides in particular encompass the following condensation products:

[0157] - at least two lactams,

[0158] - at least two aliphatic α,ω-amino carboxylic acids,

[0159] - at least one lactam and at least one aliphatic α,ω-amino carboxylic acid,

[0160] - at least two diamines and at least two diacids,

[0161] - at least one lactam with at least one diamine and at least one diacid,

[0162] - at least one aliphatic α,ω-amino carboxylic acid with at least one diamine and at least one diacid,

[0163] The one or more diamines and the one or more diacids may independently of one another be aliphatic, cycloaliphatic or aromatic.

[0164] Depending on the type and proportion of the monomers, the copolyamide can be semi-crystalline or amorphous. Among amorphous copolyamides, mention may be made, for example, of copolyamides containing semi-aromatic monomers.

[0165] Semi-crystalline copolyamides can also be used, in particular copolyamides PA 6 / 11, PA 6 / 12 and PA 6 / 11 / 12.

[0166] The number-average molecular weight Mn of the copolyamide, as measured according to standard ISO 16014-5:2019, can vary within a wide range, but it is advantageously less than 10,000 g / mol.

[0167] Advantageously, the polyamide graft is monofunctional.

[0168] In order to make the polyamide graft have a monoamine end group, a chain terminator of the following formula can be used:

[0169] R1R2NH

[0170] where:

[0171] • R1 is hydrogen or a straight-chain or branched-chain alkyl group containing at most 20 carbon atoms,

[0172] •R2 is a straight-chain or branched-chain alkyl or alkenyl group containing up to 20 carbon atoms, a saturated or unsaturated alicyclic group, an aromatic group, or a combination thereof. The chain limiter can be, for example, laurylamine or oleylamine.

[0173] To make the polyamide graft have a monocarboxylic acid end group, a chain limiter of the formula R'1-COOH, R'1-CO-O-CO-R'2 or a dicarboxylic acid can be used.

[0174] R'1 and R'2 are straight-chain or branched-chain alkyls containing up to 20 carbon atoms.

[0175] Advantageously, the polyamide graft has a terminal with an amine functional group. Preferred polymerized monofunctional chain limiters are laurylamine and oleylamine.

[0176] Advantageously, the polyamide graft has a molar mass of 1000 - 5000 g / mol, preferably 2000 - 3000 g / mol.

[0177] The polycondensation defined above is carried out according to known methods, for example, at a temperature of 200 - 300 °C, under vacuum or in an inert atmosphere, with stirring of the reaction mixture. The average chain length of the graft is determined by the initial molar ratio between the polycondensable monomer or lactam and the chain limiter. To calculate the average chain length, usually one chain limiter molecule is counted for each graft chain.

[0178] By selecting appropriate monomer types and ratios, polyamide grafts with the desired glass transition temperature and melting temperature (if any) can be prepared. The viscosity of the polyamide graft can be adjusted by regulating the molar mass of the polyamide graft.

[0179] The condensation reaction of the polyamide graft on the polyolefin backbone containing the residue of (X) is carried out by the reaction of the amine or acid functional group of the polyamide graft on the residue of (X). Advantageously, a monoamine polyamide graft is used, and an amide or imide bond is formed by reacting the amine functional group with the functional group of the residue of (X).

[0180] This condensation is preferably carried out in the molten state.

[0181] Conventional mixing and / or extrusion techniques can be used to manufacture the composition. Thus, the components of the composition are mixed to form a compound that can optionally be granulated at the die outlet. Advantageously, a coupling agent is added during compounding.

[0182] To obtain a nanostructured composition, the polyamide grafts and the backbone can thus be mixed in an extruder at a temperature generally between 200 °C and 300 °C. The average residence time of the melt in the extruder can be between 5 seconds and 5 minutes, and preferably between 20 seconds and 1 minute. The yield of the condensation reaction is evaluated by selectively extracting the free polyamide grafts, i.e., those polyamide grafts that have not reacted to form the polyamide graft polymer.

[0183] The preparation of polyamide grafts with amine end groups and their addition to a polyolefin backbone containing residues of (X) are described in patents US 3 976 720, US 3 963 799, US 5 342 886, and FR 2 291 225. The polyamide graft polymers of the present invention advantageously have a nanostructured organization. To obtain this type of texture, grafts with a number average molar mass Mn of 1000 - 5000 g / mol, more preferably 2000 - 3000 g / mol, are preferably used, for example.

[0184] Particularly preferred polyamide graft polymers contain residues of carboxylic anhydride monomers, especially maleic anhydride monomers, and polyamide 6 (PA6) grafts.

[0185] The graft polymer comprises from 5% to 50% by weight, and preferably from 15% to 30% by weight, of polyamide grafts.

[0186] According to one embodiment, the polyamide graft polymer has a melting temperature greater than 120 °C.

[0187] Advantageously, the melting temperature of the carrier film is also higher than the melting temperature of the adhesive layer, which makes it possible to provide the structure with thermomechanical stability. Preferably, the difference between the melting temperature of the carrier film and the melting temperature of the adhesive layer is between 30 and 60 °C.

[0188] According to one embodiment, the melt flow index (MFI) of the carrier film is between 0.2 g / 10 min and 10 g / 10 min, preferably between 0.4 g / 10 min and 3 g / 10 min, and more preferably between 0.6 g / 10 min and 2 g / 10 min (230 °C, 2.16 kg, ASTM D 1238).

[0189] According to another embodiment, the thickness of the carrier film is from 15 μm to 60 μm, especially on the order of 20 μm.

[0190] As described above, the carrier film can be in direct contact with a second adhesive layer in order to form an adhesive layer / carrier film / adhesive layer three-layer structure, the second adhesive layer being the same as or different from the first adhesive layer as previously defined.

[0191] B. Method for preparing a multi-layer structure

[0192] The multi-layer structure according to the invention can be obtained from a mixture intended for the adhesive layer and the carrier film via conventional techniques for producing films, sheets or plates.

[0193] By way of example, mention may be made of the techniques of extrusion blow molding of a sheath (also known as "blown film"), extrusion lamination, extrusion coating, extrusion of a flat film (also known as "cast film") or even extrusion of a sheet. All these techniques are known to those skilled in the art and he will be able to adjust the operating conditions of the various techniques (temperature of the extruder, connector, die and feedblock, rotation speed of the screw, cooling temperature of the cooling cylinder, etc.) to form a structure according to the invention having the desired shape and thickness. The invention is not departed from if the final structure is obtained by a pressing technique, by adhesive lamination via a solvent-based or aqueous route, or if the final structure undergoes an additional annealing step.

[0194] The multi-layer structure is preferably prepared by coextrusion, in particular by coextrusion of a flat film.

[0195] During the coextrusion of two layers, the layer of the carrier film is generally heated to a temperature higher than the temperature of the adhesive layer so that their viscosities are as close as possible at their respective temperatures.

[0196] C. Use for manufacturing a photovoltaic module

[0197] According to a second aspect, the invention relates to the use of a multi-layer structure as defined above for manufacturing a photovoltaic module.

[0198] The multi-layer structure according to the invention is of interest in the present application because it greatly facilitates the assembly of the photovoltaic cell with the encapsulant and the upper protective layer (called the front plate) and the back of the module (called the backsheet). In particular, the structure is suitable for manufacturing a module as described in patent application WO 2004 / 021455, which requires direct lamination of the encapsulant onto the surface of the interconnect. Specifically, the good adhesion of the metal of the adhesive layer of the multi-layer structure according to the invention allows the interconnect to be pre-laminated onto the multi-layer structure, which makes the assembly of the photovoltaic module simpler.

[0199] It may be advantageous to use the multi-layer structure according to the invention together with a coated interconnect. In particular, the interconnect can be coated with a material having a melting temperature lower than the melting temperature of the adhesive layer, which helps with welding to the photovoltaic cell.

[0200] In this use, it is particularly advantageous that the carrier film forms a protective layer on the back of the photovoltaic module called the "backsheet".

[0201] D. Photovoltaic module

[0202] According to yet another aspect, the present invention relates to a photovoltaic module comprising at least one multi-layer structure as described above.

[0203] The multi-layer structure can in particular be used as an encapsulant for at least one photovoltaic cell (10). Additionally, according to a preferred embodiment, the carrier film of the multi-layer structure can be used as a protective layer on the back side of the module ("backsheet") (26).

[0204] E. Method for manufacturing a photovoltaic module

[0205] According to yet another aspect, the present invention relates to a method for preparing a photovoltaic module, which comprises the step of encapsulating at least one photovoltaic cell (10) with a multi-layer structure as previously defined.

[0206] The multi-layer structure, more particularly its adhesive layer, is in direct contact with the photovoltaic cell (10), in particular with at least one electrical interconnector (18) connecting two photovoltaic cells (12).

[0207] According to one embodiment, the step of encapsulating at least one photovoltaic cell (10) comprises the following steps:

[0208] (i) At a temperature below the melting temperature of the adhesive layer (22), in particular at a temperature 5 to 20 °C below the melting temperature of the adhesive layer (22), typically at a temperature between 70 and 80 °C, the adhesive layer (22) of the multi-layer structure is placed in contact with at least one electrical interconnector (18), thereby obtaining at least one electrical interconnector (18) fixed to the surface of the adhesive layer of the multi-layer structure;

[0209] (ii) At a temperature between the melting temperature of the adhesive layer and the flow temperature of the backsheet, in particular between 140 and 160 °C, the multi-layer structure layer having at least one electrical interconnector fixed in the previous step is laminated to the other components of the photovoltaic cell (10).

[0210] According to a particular embodiment, the electrical interconnectors (18) can in particular be arranged in the form of parallel lines or strips on the surface of the adhesive layer (22) of the multi-layer structure. They can be fixed to the surface of the adhesive layer (22) by contacting the adhesive layer (22), and the adhesive layer (22) can have been heated to a temperature between 50 °C and 100 °C to make it sticky. Then, the multi-layer structure containing the interconnectors (18) obtained in step i) can be placed on the other components of the photovoltaic module, in particular on the photovoltaic cell (10).

[0211] To facilitate the assembly of the module, the interconnectors can be coated with a polymer having a temperature lower than that of the adhesive layer.

[0212] Preferably, at room temperature, the peel strength of the interface between the adhesive layer (22) and the wire used as an electrical interconnector (18) in the module is at least 0.1 N / cm at an angle of 90°, preferably at least 0.2 N / cm.

[0213] Examples

[0214] Materials used

[0215] Polyolefin A

[0216] AAffinity PL1880 g: Ethylene-octene copolymer, sold by Dow Chemicals

[0217] BEVA 1010 VN3: Ethylene and vinyl acetate copolymer, sold by Total

[0218] CLDPE 1022 FN24: Linear low density polyethylene, sold by Total

[0219] Functional polyolefin

[0220] Lotader® 3210: Terpolymer of ethylene, butyl acrylate and maleic anhydride, sold by SK Functional Polyolefins

[0221] Additive

[0222] - Adhesive masterbatch MB4 sold by Arkema France: Adhesion promoter on glass containing silane

[0223] - Masterbatch UVB: Masterbatch containing UV stabilizer

[0224] Apolhya Solar® LP91H3-UVB, which comprises 80 wt% of a polyolefin forming a backbone having maleic anhydride functional groups grafted to 20 wt% of polyamide 6. The product has an MFI (melt flow index) of 0.5 g / 10 min at 230 °C at 2.16 kg and a melting point of 216 °C.

[0225] Apolhya Solar® LC3-UV, which comprises 80 wt% of a polyolefin forming a backbone having maleic anhydride functional groups grafted to 20 wt% of copolyamide 6.12. The product has an MFI (melt flow index) of 10 g / 10 min at 230 °C at 2.16 kg and a melting point of 130 °C.

[0226] [Table 1]

[0227]

[0228] Preparation of the film

[0229] A 70 μm thick film was prepared by flat film extrusion (casting) on a Dr COLLIN brand extrusion production line. This extrusion line consists of three extruders equipped with a standard polyolefin screw profile, a variable coextrusion block (variable feed block), and a 250 mm frame die. The coextrusion block allows the production of a double-layer film (layer 1 / layer 2) with a variable thickness distribution.

[0230] Examples 1 to 3

[0231] The adhesive layer formulation was prepared by dry blending the functionalized polyolefin and polyolefin A as shown in Table 1 above. Then, a film comprising an adhesive layer and a carrier film was prepared by coextrusion according to the instructions in Table 1 under the following conditions:

[0232] - Extrusion temperature of the adhesive layer: 150 °C,

[0233] - Extrusion temperature of the carrier film: 240 °C,

[0234] - Temperature of the coextrusion head and die: 220 °C,

[0235] - Line speed: 6 m / min.

[0236] Example 4 (comparative)

[0237] A film as shown in the foregoing examples was prepared by coextrusion, except that the formulation of functionalized polyolefin and polyolefin A was replaced with APolhya Solar LC3-UV.

[0238] Example 5 (comparative)

[0239] A single-layer film of APolhya Solar LP91H3-UVB was prepared by extrusion under the following conditions:

[0240] - Extrusion, coextrusion head and die temperature: 240 °C,

[0241] - Line speed: 6 m / min.

[0242] Film evaluation

[0243] The films were characterized by measuring the melting temperature of the adhesive layer by DSC according to standard ISO11357-1 / -3.

[0244] In addition, the adhesion between the wire used as the connection of the photovoltaic module and the film was evaluated according to the following protocol:

[0245] - Ten tin wires with a diameter of 25 μm were placed side by side in parallel contact with the adhesive layer of the film;

[0246] - Welding was carried out by pressing at 5 bar for 2 s at 130 °C; and

[0247] - The adhesion between the wire and the film was evaluated using a dynamometer by a free-angle peel test, where the wire was held by one jaw and the film was held by the other jaw. The balance force during the delamination expansion process was measured.

[0248] The results of these evaluations are given in Table 2 below.

[0249] [Table 2]

[0250]

[0251] These results show that the multi-layer structure according to the invention is characterized by a higher peel force than the peel force obtained by a structure in which the adhesive layer does not contain the combination of the functional polyolefin / and polyolefin A as defined in the present invention, but a polyamide-grafted polyolefin with a melting point of 130 °C (Example 4) or a single-layer structure (Example 5).

[0252] Furthermore, these results show that an adhesive layer matrix with a melting point between 80 °C and 120 °C can significantly increase the adhesion to the metal wire.

Claims

1. A multi-layer structure comprising an adhesive layer and a layer forming a carrier film in direct contact with the adhesive layer, wherein (a) the adhesive layer comprises: - Polyolefin A, which is selected from homopolymers of ethylene and copolymers of ethylene and α-olefins, copolymers of ethylene and vinyl esters of carboxylic acids, especially ethylene-vinyl acetate (EVA), or (co)polymers comprising units of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, isobutyl (meth)acrylate or tert-butyl (meth)acrylate; and - A functionalized polyolefin different from Polyolefin A, which comprises a polyolefin backbone containing residues of at least one unsaturated monomer (Y), and the residues of the unsaturated monomer (Y) are fixed to the backbone by grafting or copolymerization; the melting temperature of the adhesive layer is between 80°C and 120°C, (b) the carrier film comprises a polyamide graft polymer, and the polyamide graft polymer comprises: - A polyolefin backbone and at least one polyamide graft, the polyolefin backbone accounting for 50% to 95% by mass of the polyamide graft polymer and containing residues of at least one unsaturated monomer (X), and the polyamide graft accounting for 5% to 50% by mass of the polyamide graft polymer, wherein: o The polyamide graft is connected to the polyolefin backbone through residues of the unsaturated monomer (X), and the residues of the unsaturated monomer (X) contain functional groups capable of reacting through a condensation reaction with a polyamide having at least one amine terminal and / or at least one carboxylic acid terminal, o The residues of the unsaturated monomer (X) are fixed to the backbone by grafting or copolymerization, o The polyolefin backbone and the polyamide graft are selected such that the polyamide graft polymer has a flow temperature greater than 160°C measured by DSC according to ISO 11357-1:2016, ISO 11357-2:2020, ISO 11357-3:2018, and the flow temperature is defined as the highest temperature among the melting temperature and the glass transition temperature of the polyamide graft and the polyolefin backbone.

2. The multi-layer structure according to claim 1, wherein the melting temperature of the adhesive layer is between 90°C and 110°C.

3. The multi-layer structure according to any one of the preceding claims, wherein the adhesive layer has a melt flow index (MFI) of 0.2 g / 10 min to 10 g / 10 min, preferably 0.4 g / 10 min to 3 g / 10 min, and especially 0.6 g / 10 min to 2 g / 10 min measured at 190°C under 2.16 kg according to ASTM standard D 1238.

4. The multi-layer structure according to any one of claims 1 to 3, wherein the adhesive layer comprises: - 65% to 95% by weight of Polyolefin A; - 5% to 35% by weight of functional polyolefin; and - 0 to 5% by weight of one or more additives.

5. The multilayer structure according to any one of claims 1 to 4, wherein the adhesive layer has a thickness of 20 to 60 μm.

6. The multilayer structure according to any one of claims 1 to 5, wherein the carrier film has a thickness of 5 μm to 40 μm.

7. The multilayer structure according to any one of claims 1 to 6, wherein the comonomer of the α-olefin of polyolefin A in the adhesive layer is selected from ethylene-propylene, ethylene-butene, and ethylene-octene.

8. The multilayer structure according to any one of claims 1 to 7, wherein the functional polyolefin of the adhesive layer is a polyolefin containing the residue of at least one unsaturated monomer (Y), and the unsaturated monomer (Y) is maleic anhydride.

9. The multilayer structure according to any one of claims 1 to 8, wherein the carrier film has a melt flow index (MFI) measured at 230 °C under 2.16 kg according to ASTM standard D1238 between 0.2 g / 10 min and 10 g / 10 min, preferably between 0.4 g / 10 min and 3 g / 10 min, particularly between 0.6 g / 10 min and 2 g / 10 min.

10. The multilayer structure according to any one of claims 1 to 9, characterized in that The carrier film has the adhesive layer on one of its surfaces.

11. The multi-layer structure according to any one of claims 1 to 9, characterized in that The carrier film has the adhesive layer on both of its surfaces.

12. A method for preparing the multilayer structure according to any one of claims 1 to 11, wherein the carrier film is assembled to the adhesive layer by coextrusion.

13. Use of the multilayer structure according to any one of claims 1 to 11 for manufacturing a photovoltaic module.

14. A method for preparing a photovoltaic module, wherein a photovoltaic cell is encapsulated with the multilayer structure according to any one of claims 1 to 11.

15. The method according to claim 14, wherein the encapsulation comprises the following steps: (i) Fixing a conductive wire to the surface of the adhesive layer of the multilayer structure according to any one of claims 1 to 11 at a temperature lower than the melting temperature of the adhesive layer to form an assembly; (ii) Contacting the assembly with a photovoltaic cell at a temperature between the melting temperature of the adhesive layer and the flow temperature of the carrier film.

16. A photovoltaic module, comprising the multilayer structure as defined in any one of claims 1 to 11.

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