Ethylene / α-olefin copolymer for solar cell membranes, method of preparing this copolymer, preparation for solar cell membranes, solar cell membranes, method of producing these membranes, and solar cell modules.

Abstract

The invention relates to an ethylene / α-olefin copolymer for solar cell cladding, a method for preparing this copolymer, a composition for solar cell cladding, solar cell cladding, a method for producing this cladding, and a solar cell module. The use of the ethylene / α-olefin copolymer proposed in the invention in solar cell cladding can take into account both the relatively high vulcanization reaction rate and the good anti-PID properties of the solar cell cladding. The ethylene / α-olefin copolymer for solar cell cladding satisfies the following conditions (a) to (c): (a) under angular frequency conditions between 0.1 and 500 rad / sec, the characteristic elongation time at 190℃ is between 200.0 and 500.0 milliseconds; (b) the average molecular weight is between 20,000 and 200,000 g / mol, the density is between 0.850 and 0.910 g / cm3; and (c) the molecular weight distribution is between 1.5 and 3.

Description

Ethylene / α-olefin copolymer for solar cell encapsulation film and its application Technical Field

[0001] The present invention relates to the technical field of solar cell encapsulation films, and in particular to an ethylene / α-olefin copolymer for solar cell encapsulation films and applications thereof. Background Art

[0002] Photovoltaic power generation, one of the most competitive forms of renewable energy, is expected to expand rapidly in the future. The corresponding encapsulating film materials, ethylene-vinyl acetate (EVA) and ethylene / α-olefin copolymer (POE), account for a small portion of the total cost of photovoltaic modules, approximately 7%, but they are a key factor in determining the quality and lifespan of photovoltaic modules. Once the film and backsheet of a battery module begin to yellow and crack, the battery is prone to premature failure. Photovoltaic modules are used in high-voltage environments for a long time, and wet leakage current channels are easily generated between the encapsulating material, backsheet, glass, and frame. Large amounts of charge accumulate on the surface of the cell, causing significant surface passivation and leading to a significant performance degradation of the module, a phenomenon known as PID.

[0003] Currently, the mainstream approaches to achieving PID-resistant films are: 1. Using polyolefin elastomer (POE) materials with lower water permeability instead of EVA; 2. Adding additional PID-resistant additives to the formulation. However, both approaches have drawbacks: the inherent PID-resistant properties of POE films still need to be improved; and the addition of inorganic additives can affect the film's optical properties, leading to increased haze. Patent applications CN112898920A, CN113234402A, and CN113122164B achieve PID-resistant films by adding inorganic and organic small molecule additives. However, the introduction of these additives is often accompanied by the problem of additive precipitation, which affects the long-term performance of the encapsulating film. Patent application CN112824466A introduces a co-crosslinker into the photovoltaic film formulation, increasing the crosslink density of the crosslinked encapsulating film and enhancing its metal ion barrier, thereby achieving PID-resistant results. However, these approaches represent formulation optimizations and do not address the encapsulating material itself.

[0004] Another important aspect is that, based on the downstream film processing needs, how to increase the vulcanization speed of photovoltaic films, thereby shortening the processing time of the lamination cross-linking reaction and achieving greater cost reduction and efficiency improvement, is an issue that the industry urgently needs to solve. The existing solution to speed up the vulcanization speed of POE photovoltaic films is mainly to modify the POE particles through formula optimization or silane grafting. Patent application CN116023891A uses chemical grafting modification to graft silane monomers onto POE macromolecular chains to form a high molecular weight thickener, thereby contributing to the cross-linking degree of film curing through silane cross-linking, increasing the cross-linking speed of the film and shortening the curing cycle. Patent application CN115873528A optimizes the film cross-linking formula to accelerate the cross-linking speed and improve the production efficiency of the components. Patent application CN116004126A improves the cross-linking properties by changing the layer structure of the encapsulation film, thereby comprehensively improving the encapsulation effect of POE applied in components. Overall, there are few reports and applications of using pure POE particles as a starting point to improve the cross-linking and vulcanization speed and anti-PID performance of photovoltaic films.

[0005] In summary, it is very necessary to provide a solution that can achieve both a faster vulcanization reaction speed and good anti-PID performance without upgrading the solar cell encapsulation film formula.

[0006] Summary of the Invention

[0007] The present invention provides an ethylene / α-olefin copolymer for use in a solar cell encapsulation film and its application. The ethylene / α-olefin copolymer provided by the present invention is used in a solar cell encapsulation film, achieving both a relatively fast vulcanization reaction rate and good PID resistance.

[0008] To achieve its purpose, the present invention provides the following technical solutions:

[0009] In one aspect, the present invention provides an ethylene / α-olefin copolymer for solar cell encapsulation film, wherein the copolymer satisfies the following conditions (a) to (c):

[0010] (a) Characteristic relaxation time at 190°C is 200.0–500.0 ms under angular frequency conditions of 0.1–500 rad / s;

[0011] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0012] (c) The molecular weight distribution is 1.5-3.

[0013] Preferably, the characteristic relaxation time is 350.0-500.0 milliseconds, more preferably 400-500 milliseconds.

[0014] Furthermore, the copolymer has a melt index of 1 g / 10 min to 50 g / 10 min at 190° C. and a load of 2.16 kg.

[0015] In some embodiments, the weight average molecular weight is 40,000-100,000 g / mol.

[0016] In some embodiments, the α-olefin includes one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene.

[0017] A second aspect of the present invention provides a method for preparing the ethylene / α-olefin copolymer for solar cell encapsulation film, the method comprising the following steps:

[0018] (S1) polymerizing ethylene and α-olefin to obtain a copolymer;

[0019] (S2) post-treating the copolymer product to separate therefrom an ethylene / α-olefin copolymer that simultaneously satisfies conditions (a) to (c):

[0020] (a) a characteristic relaxation time at 190° C. of 200.0 to 500.0 milliseconds, preferably 350.0 to 500.0 milliseconds, and more preferably 400 to 500 milliseconds at an angular frequency of 0.1 to 500 rad / s;

[0021] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0022] (c) The molecular weight distribution is 1.5-3.

[0023] A third aspect of the present invention provides a solar cell encapsulation film composition, wherein the composition comprises the above-mentioned ethylene / α-olefin copolymer or the ethylene / α-olefin copolymer prepared by the above-mentioned preparation method.

[0024] Furthermore, the composition further comprises one or more of a cross-linking agent, a co-cross-linking agent, a coupling agent and an antioxidant.

[0025] A fourth aspect of the present invention provides a solar cell encapsulation film, which is prepared using the composition.

[0026] A fifth aspect of the present invention provides a method for preparing the solar cell encapsulation film, comprising the following steps:

[0027] The components of the composition are mixed and melted, extruded and cast into a film, and then cooled and cut.

[0028] A sixth aspect of the present invention provides a solar cell assembly, which includes the aforementioned solar cell encapsulation film.

[0029] The technical solution provided by the present invention has the following beneficial effects:

[0030] The ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention satisfies the above conditions (a) to (c) at the same time and has a relatively high characteristic relaxation time. The copolymer enables the solar cell encapsulation film to have both a relatively fast vulcanization reaction speed and good anti-PID performance. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0033] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. Reagents or instruments used without specifying the manufacturer are all commercially available conventional products.

[0034] The ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention satisfies the following conditions (a) to (c) at the same time:

[0035] (a) Characteristic relaxation time at 190°C is 200.0–500.0 ms under angular frequency conditions of 0.1–500 rad / s;

[0036] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0037] (c) The molecular weight distribution is 1.5-3.

[0038] The ethylene / α-olefin copolymer for solar cell encapsulation film of the present invention has the following characteristic (a): under the angular frequency condition of 0.1-500 rad / s, the characteristic relaxation time at 190°C is greater than or equal to 200.0 milliseconds and less than or equal to 500.0 milliseconds, for example, 200.0 milliseconds, 250.0 milliseconds, 300.0 milliseconds, 350.0 milliseconds, 400.0 milliseconds, 450.0 milliseconds, 500.0 milliseconds, etc.; preferably, the characteristic relaxation time is 350.0-500.0 milliseconds, more preferably 400-500 milliseconds.

[0039] In addition to the above-mentioned characteristic relaxation time, the ethylene / α-olefin copolymer for solar cell encapsulation film of the present invention also has the following characteristics (b) and (c): (b) a weight-average molecular weight of 20,000-200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc; (c) a molecular weight distribution of 1.5-3.

[0040] The use of an ethylene / α-olefin copolymer having the above characteristics (a)-(c) to prepare a solar cell encapsulation film can achieve both a short vulcanization reaction time and good anti-PID performance.

[0041] The ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention has a weight average molecular weight (M w ) is 20,000-200,000 g / mol, for example, 40,000-100,000 g / mol, for example, 40,000-90,000 g / mol, and further for example, 45,000-75,000 g / mol.

[0042] The ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention has a density of 0.850 g / cc to 0.910 g / cc, for example, 0.850 g / cc, 0.860 g / cc, 0.870 g / cc, 0.880 g / cc, 0.890 g / cc, 0.900 g / cc, 0.905 g / cc, 0.910 g / cc, etc.

[0043] The ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention has a molecular weight distribution (PDI) of 1.5-3, such as 1.5, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, etc., and further such as 2.1-2.8.

[0044] In addition, the ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention has a melt index (MI) of 1 g / 10 min to 50 g / 10 min at 190° C. and 2.16 kg load, for example, 1 g / 10 min, 2 g / 10 min, 3 g / 10 min, 5 g / 10 min, 10 g / 10 min, 15 g / 10 min, 17 g / 10 min, 20 g / 10 min, 25 g / 10 min, 30 g / 10 min, 40 g / 10 min, 45 g / 10 min, 50 g / 10 min, etc., for example, 2 g / 10 min to 40 g / 10 min, for example, 2 g / 10 min to 20 g / 10 min, and further for example, 3 g / 10 min to 17 g / 10 min.

[0045] The ethylene / α-olefin copolymer of the present invention can be a random or block polymer, wherein the α-olefin is derived from an α-olefin as a comonomer, and the α-olefin can include, for example, a mixture of one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-eicosene.

[0046] Characteristic Relaxation Time (CRT) refers to the time it takes to restore the stress equilibrium state in a polymer after a constant deformation has been applied to it. The CRT is related to the entanglement structure of the polymer chains. If a polymer has long-chain branches, the degree of chain entanglement increases with the increase in branched structures, thereby prolonging the polymer's CRT. At the same time, the increased degree of chain entanglement increases the free volume of the polymer chains, making this portion of the polymer more susceptible to solvation in solvents, thereby enhancing its solubility. Therefore, in actual production applications, it has the ability to be separated, that is, a polymer with target characteristics can be obtained through a dissolution-precipitation-separation method.

[0047] The present invention also provides a method for preparing the ethylene / α-olefin copolymer for solar cell encapsulation film. The ethylene / α-olefin copolymer provided by the present invention can be prepared by a preparation method comprising the following steps: (S1) polymerizing ethylene and α-olefin to obtain an ethylene / α-olefin copolymer product; (S2) post-treating the copolymer product to separate therefrom an ethylene / α-olefin copolymer that satisfies conditions (a) to (c) at the same time:

[0048] (a) a characteristic relaxation time at 190° C. of 200.0 to 500.0 milliseconds, preferably 350.0 to 500.0 milliseconds, and more preferably 400 to 500 milliseconds at an angular frequency of 0.1 to 500 rad / s;

[0049] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0050] (c) The molecular weight distribution is 1.5-3.

[0051] In some embodiments, step (S2) of post-treating the copolymerization product specifically comprises the following steps:

[0052] (S2a) dissolving the obtained copolymer product in a first good solvent, then adding the resulting solution to a first poor solvent for precipitation separation, obtaining a first liquid phase, and removing the solvent from the first liquid phase to obtain the desired product. Furthermore, step (S2b) may be performed: dissolving the precipitate obtained by precipitation separation in step (S2a) in a second good solvent, then adding the resulting solution to a second poor solvent for precipitation separation, obtaining a second liquid phase, and removing the solvent from the second liquid phase to obtain the desired product.

[0053] Step (S1):

[0054] Step (S1) is a step of preparing an ethylene / α-olefin copolymer by polymerizing ethylene and α-olefin.

[0055] In step (S1), solution polymerization can be specifically used. As a reference example, step (S1) may include the following steps: in a reactor, an organic solvent and an α-olefin are fed into the reactor by solution polymerization, a main catalyst and a co-catalyst are added to the reactor at a desired reaction temperature, and ethylene gas is fed into the reactor for reaction to obtain a reactant solution; wherein the polymerization monomer (α-olefin and / or ethylene) can be fed in a one-step or multi-step manner to control polymer index parameters, such as weight-average molecular weight, molecular weight distribution, α-olefin copolymer content, etc.; after removing the solvent from the obtained reactant solution, an ethylene / α-olefin copolymer product is obtained. The reactor used may be a reactor conventionally used in the art, such as a ring reactor, an isothermal reactor, a stirred tank reactor, a batch reactor, a circulating tubular reactor, etc. The reactor may include one or more reactors in parallel, in series, and / or in any other combination; the reaction may be carried out continuously or intermittently.

[0056] Furthermore, the organic solvent used for the polymerization reaction in step (S1) may be one or more of an aliphatic solvent and an aromatic solvent. Preferably, the aliphatic solvent is selected from one or more of n-butane, isobutane, n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, and alkylated compounds thereof. Preferably, the aromatic solvent is selected from one or more of benzene, toluene, xylene, and halogenated compounds thereof, wherein the halogenated compound may be a monohalogenated compound or a polyhalogenated compound.

[0057] Further, the main catalyst used for the polymerization reaction in step (S1) is preferably one or more of a metallocene catalyst and a post-metallocene catalyst, preferably one or more of dimethylsilyl tert-butylamine tetramethylcyclopentadiene titanium dichloride, bis (methylcyclopentadiene) zirconium dichloride, bis (1,3-dimethylcyclopentadienyl) zirconium dichloride, cyclopentadienyl-(1,2-dimethoxyethane) zirconium trichloride, dimethylsilyl bis (2-methyl-4-phenylindenyl) zirconium dichloride. Those skilled in the art can determine the specific amount of the main catalyst as needed for the reaction. For example, in some embodiments, the amount of the main catalyst can be 1-20 μmol / L relative to the amount of the reaction system solvent.

[0058] Furthermore, the co-catalyst used in the polymerization reaction in step (S1) is preferably at least one of an alkyl aluminum, an organic boron compound, and an alkyl aluminoxane, preferably one or more of methyl aluminoxane, modified methyl aluminoxane, ethyl aluminoxane, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, and tris(pentafluorophenyl) boron compound. The molar ratio of aluminum in the co-catalyst to the main catalyst metal atom may be 1 to 1000:1, and the molar ratio of boron in the co-catalyst to the main catalyst metal atom may be 0 to 5:1.

[0059] Furthermore, in step (S1), the reaction temperature is, for example, 100-210°C, such as 120-210°C, and the reaction pressure is, for example, 20-100 bar.

[0060] Step (S2a) and step (S2b):

[0061] Steps (S2a) and (S2b) are steps of post-treating the ethylene / α-olefin copolymer product obtained in step (S1) to prepare the ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention.

[0062] In step (S2a), the first good solvent used refers to a solvent that can completely dissolve the copolymerization product in step (S1). In step (S2b), the second good solvent used refers to a solvent that can completely dissolve the precipitated portion obtained in step (S2a). Specifically, the first good solvent and the second good solvent can be one or more of an aliphatic solvent and an aromatic solvent, respectively. Preferably, the aliphatic solvent is selected from one or more of n-butane, isobutane, n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane and alkylated compounds thereof. Preferably, the aromatic solvent is selected from one or more of benzene, toluene, xylene and halogenated compounds thereof, wherein the halogenated compound can be a monohalogenated compound or a polyhalogenated compound. The dissolution operation using the first good solvent or the second good solvent can be carried out at 60-140° C., and the dissolution operation can be carried out under stirring; when dissolving with the first good solvent, the mass ratio of the copolymer product to the solvent is, for example, 1:3 to 1:8; when dissolving with the second good solvent, the mass ratio of the precipitated part to the solvent is, for example, 1:3 to 1:8.

[0063] In step (S2a), the first poor solvent used can be an alcohol having 2-20 carbon atoms. It is preferably a mixture of one or more of ethanol, ethylene glycol, n-propanol, glycerol, n-butanol, neopentyl alcohol, 1,6-hexanediol, n-octanol, n-decanol, dodecanol, tetradecyl alcohol, and hexadecanol. The amount of the first poor solvent used can be 1-5 times the mass of the first good solvent in which the polymer is completely dissolved. The conditions for precipitation separation with the first poor solvent can be, for example, at room temperature or 18-22°C, in a solution in which the first good solvent in which the polymer is completely dissolved, gradually adding the first poor solvent and continuously stirring (the speed is, for example, 200-400rpm) until no polymer precipitates are precipitated in the solution. Afterwards, the polymer precipitate in the solution is filtered and separated, and then the solution is partially evaporated to remove the solvent to obtain the ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention.

[0064] The second poor solvent used in step (S2b) can be a mixed solution of alcoholic solvent and ketone solvent.Wherein alcoholic solvent can be the alcohol with 2-20 carbon atom, preferably ethanol, ethylene glycol, n-propyl alcohol, glycerol, n-butanol, neopentyl alcohol, 1,6-hexanediol, n-octanol, n-decanol, dodecanol, tetradecyl alcohol, hexadecanol or one or more mixtures thereof.Ketone solvent is preferably dimethyl ketone, diethyl ketone, butanone, methyl isobutyl ketone, valerophenone, 3-methyl-2-octanone, methyl n-nonyl ketone, methyl hexanophenone, dicyclo [3.3.1] nonyl-3,7-diketone, dimethyl cyclohexanedione, 2,2,6-trimethyl-1,4-cyclohexanedione, diphenyl ethanedione, 3-methyl-2,4-nonanedione, 1-phenyl-2,4-pentanedione, 2,4-decanedione or one or more mixtures thereof. Preferably, the mass ratio of the alcohol solvent to the ketone solvent can be 4-10:1; the amount of the second poor solvent can be 1-5 times the mass of the second good solvent in which the polymer is completely dissolved. In step (S2b), the precipitation separation can be carried out at room temperature, or at 18-22°C. In the solution in which the second good solvent in which the polymer is completely dissolved, the second poor solvent is gradually added and continuously stirred (for example, at a speed of 200-400 rpm) until no more polymer precipitates are precipitated in the solution. After that, the polymer precipitate in the solution is filtered and separated, and the solution is partially evaporated to remove the solvent to obtain the ethylene / α-olefin copolymer for solar cell encapsulation film provided by the present invention.

[0065] By processing the precipitated portion of step (S2a) through step (S2b), the ethylene / α-olefin copolymer for solar cell encapsulation film of the present invention that meets conditions (a) to (c) can be obtained.

[0066] The present invention also provides a solar cell encapsulation film composition, comprising the ethylene / α-olefin copolymer for solar cell encapsulation film or the ethylene / α-olefin copolymer for solar cell encapsulation film prepared by the preparation method. Specifically, the ethylene / α-olefin copolymer satisfies the following conditions (a) to (c) simultaneously:

[0067] (a) a characteristic relaxation time at 190° C. of 200 to 500 milliseconds, preferably 350.0 to 500.0 milliseconds, and more preferably 400 to 500 milliseconds at an angular frequency of 0.1 to 500 rad / s;

[0068] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0069] (c) The molecular weight distribution is 1.5-3.

[0070] The specific contents of the ethylene / α-olefin copolymer in the above composition can be referred to the corresponding description of the ethylene / α-olefin copolymer for photovoltaic encapsulation film provided by the present invention in the above text, and will not be repeated here.

[0071] The composition adopts the ethylene / α-olefin copolymer for photovoltaic encapsulation film provided by the present invention, which can significantly shorten its vulcanization reaction time and give the obtained encapsulation film excellent anti-PID performance.

[0072] The solar cell encapsulation film composition may further include other components conventionally added in the art, specifically, for example, one or more of a crosslinking agent, a co-crosslinking agent, a coupling agent, and an antioxidant. Of course, other additional components permitted in the art may also be included.

[0073] Further, the cross-linking agent can be a peroxide cross-linking agent, including but not limited to one or more combinations of the following compounds: tert-butyl peroxy isopropyl carbonate, 2,5-dimethyl-2,5-(bis-tert-butylperoxy)hexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-amylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane, tert-butyl peroxy 2-ethylhexyl carbonate, tert-amyl peroxy carbonate, tert-butyl peroxy 3,3,5-trimethylhexanoate. The crosslinking agent may be used in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the ethylene / α-olefin copolymer.

[0074] Furthermore, the auxiliary cross-linking agent can be a combination of one or more multifunctional acrylate substances, including but not limited to a combination of one or more of the following substances: triallyl isocyanurate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, tris(2-hydroxyethyl)isocyanuric acid triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, pentaerythritol tetrapropylene glycol, propylene glycol triacrylate ... The crosslinking aid may be used in an amount of 0.1 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the ethylene / α-olefin copolymer.

[0075] Furthermore, the coupling agent can be a silane coupling agent, including but not limited to a combination of one or more of the following compounds: γ-methacryloxypropyltrimethoxysilane, γ-chloropropylmethoxysilane, vinylethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidyloxypropyltrimethoxysilane, 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate, anilinemethyltriethoxysilane, octyltrimethoxysilane. Based on 100 parts by weight of the ethylene / α-olefin copolymer, the amount of the coupling agent can be 0.1-3 parts by weight, preferably 0.1-0.6 parts by weight.

[0076] Furthermore, the antioxidant can be a combination of one or more of a hindered phenol antioxidant and a phosphate antioxidant, including but not limited to a combination of one or more of the following compounds: β-[3,5-di-tert-butyl-4-hydroxyphenyl] propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, bis(3,5-di-tert-butyl-4-hydroxypropionyl)hydrazine, 2,2'-oxalyl-bis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, N,N'-hexamethylenebis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, (3,5-di-tert-butyl-4-hydroxyphenylpropionamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)trione, triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 4,6-bis(octylthiomethyl)-o-cresol, tris[2,4-di-tert-butylphenyl]phosphite, bis[2,4-di-tert-butylphenyl]pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphate. Based on 100 parts by weight of the ethylene / α-olefin copolymer, the antioxidant can be used in an amount of 0.01-1 part by weight, preferably 0.05-0.5 part by weight.

[0077] In some embodiments, the solar cell encapsulation film composition, based on 100 parts by weight of ethylene / α-olefin copolymer, further includes 0.1-5 parts by weight of a cross-linking agent, preferably 0.5-2 parts by weight; 0.1-5 parts by weight of a co-cross-linking agent, preferably 0.1-2 parts by weight; 0.1-3 parts by weight of a coupling agent, preferably 0.1-0.6 parts by weight; and 0.01-1 parts by weight of an antioxidant, preferably 0.05-0.5 parts by weight.

[0078] The present invention also provides a solar cell encapsulation film, which is prepared using the composition described above. Specifically, the composition comprises the ethylene / α-olefin copolymer for photovoltaic encapsulation film provided by the present invention, wherein the ethylene / α-olefin copolymer satisfies the following conditions (a) to (c):

[0079] (a) a characteristic relaxation time at 190° C. of 200 to 500 milliseconds, preferably 350.0 to 500.0 milliseconds, and more preferably 400 to 500 milliseconds at an angular frequency of 0.1 to 500 rad / s;

[0080] (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc;

[0081] (c) The molecular weight distribution is 1.5-3.

[0082] The details of the composition and the ethylene / α-olefin copolymer can be referred to the above description and will not be repeated here.

[0083] The present invention also provides a method for preparing the aforementioned solar cell encapsulation film, comprising the steps of: mixing and melting the components of the composition, extruding and casting the film, and then cooling and slitting the film. Specifically, a winding step may also be included. The specific process operations and process conditions of this preparation method can be carried out in accordance with conventional methods in the art and are not particularly limited.

[0084] The solar cell encapsulation film prepared based on the ethylene / α-olefin copolymer for photovoltaic encapsulation film of the present invention can achieve both a faster vulcanization reaction speed and good anti-PID performance.

[0085] The present invention further provides a solar cell assembly, which includes the solar cell encapsulation film described above.

[0086] The present invention discovered that ethylene / α-olefin copolymers with a relatively high characteristic relaxation time inherently exhibit a high degree of chain entanglement. Compared to ethylene / α-olefin copolymers with a relatively low characteristic relaxation time, these copolymers are more likely to form bulk crosslinked structures during crosslinking reactions. This accelerates the vulcanization and crosslinking reactions, shortening processing time in downstream film factories using laminators during photovoltaic film applications and shortening the time required for the polyolefin elastomer in the film to undergo vulcanization and crosslinking reactions. Furthermore, the increased degree of chain entanglement in the polyolefin elastomer structure makes it easier for the film to form a denser crosslinked structure, thereby enhancing the film's barrier capability to metal ions and reducing the rate at which metal ions migrate to the cell surface, thereby improving the film's anti-PID performance.

[0087] The ethylene / α-olefin copolymer for photovoltaic encapsulation film provided by the present invention is an ethylene / α-olefin copolymer with a high characteristic relaxation time, which satisfies conditions (a) to (c) at the same time; the encapsulation film containing the copolymer can take into account both a fast vulcanization reaction speed and good anti-PID performance, and can be widely used in the electrical and electronic industries.

[0088] The present invention will be described in more detail below with reference to the examples provided. The examples provided are only for illustrative purposes and should not be construed as limiting the scope of the present invention.

[0089] The main raw materials are described as follows:

[0090] Tert-butyl peroxy-2-ethylhexyl carbonate, Akzo Nobel, purity >95%;

[0091] Triallyl isocyanurate, Acros, 98% purity;

[0092] γ-Methacryloxypropyltrimethoxysilane, Aladdin, purity 95%;

[0093] γ-(2,3-Epoxypropyloxy)propyltrimethoxysilane, Aladdin, purity 95%;

[0094] Bis[2,4-di-tert-butylphenyl]pentaerythritol diphosphite, Acros, purity 95%;

[0095] β-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate, ark, purity 95%;

[0096] 1,1-Bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Acros, 95% purity;

[0097] tert-Amyl peroxycarbonate, ark, purity 95%;

[0098] Trimethylolpropane triacrylate, Aladdin, 98% pure;

[0099] Antioxidant 1076, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, industrial grade, Li’anlong New Materials Co., Ltd.

[0100] Antioxidant 1010, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, Li’anlong New Materials Co., Ltd., industrial grade;

[0101] 1-Octene, Aladdin, purity 99%;

[0102] 1-Butene, Aladdin, purity 99%;

[0103] 1-Hexene, Aladdin, purity 99%;

[0104] 1-Decene, Aladdin, 99% purity;

[0105] Ethylene, open torch gas, purity 99.99%;

[0106] Methylaluminoxane, AkzoNobel, 10% wt toluene solution;

[0107] Modified methylaluminoxane (MMAO-3A), Nouryon, 7 wt% toluene solution.

[0108] Dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, Jiangsu Xinuoke Catalyst Co., Ltd., purity 98%;

[0109] Dimethylsilyl tert-butylamine tetramethylcyclopentadienyl titanium dichloride, Suzhou Yuanqi Material Technology Co., Ltd., purity 98%;

[0110] Bis(methylcyclopentadienyl)zirconium dichloride, Shanghai Mairui Biochemical Technology Co., Ltd., purity 97%;

[0111] Bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, Baoji Funuokang Industrial Co., Ltd., purity >95%;

[0112] n-Heptane, Shanghai Aladdin Biochemical Technology Co., Ltd., purity >99.5%;

[0113] n-Octane, Shanghai Aladdin Biochemical Technology Co., Ltd., purity >99.5%;

[0114] Methylhexanophenone, Jinan Hongli Chemical Co., Ltd., purity >99%;

[0115] Bicyclo[3.3.1]nonane-3,7-dione, Zhengzhou Huiju Chemical Co., Ltd., purity 98%;

[0116] 3-Methyl-2-octanone, Shanghai Haohong Biopharmaceutical Technology Co., Ltd., purity >98%;

[0117] 1-Phenyl-2,4-pentanedione, Beijing Coupling Technology Co., Ltd., purity >98%;

[0118] Alkane solvent, Tianjin Tairong, industrial grade;

[0119] Ethanol, Tianjin Tairong, industrial grade;

[0120] PERC cells, Tongwei 182 bifacial cells.

[0121] Instruments, devices and detection methods:

[0122] The extruder was a single-screw extruder (L / D = 35) with a screw diameter of 30 mm;

[0123] Characteristic relaxation time tester: TA Instruments ARES-G2 rheometer. The complex viscosity of the copolymer was obtained based on the stress-dependent change in angular frequency at 190°C, angular frequencies ranging from 0.1 rad / s to 500 rad / s, and a strain of 5%. The characteristic relaxation time λ was calculated by fitting the following Carreau-Yasuda equation: η(γ) = η ∞ +(η0-η ∞ )[1+(λγ) α ] (n-1) / α

[0124] η(γ): viscosity, unit: Pa·s

[0125] η ∞ : Infinite viscosity, unit: Pa·s

[0126] η0: Zero shear viscosity, unit: Pa·s

[0127] λ: relaxation time, unit s

[0128] γ: shear rate, unit s -1

[0129] α: material constant, a dimensionless parameter describing the transition of viscosity from the Newtonian region to the non-Newtonian region. For the Carreau model, α = 2;

[0130] n: shear thinning index.

[0131] PID aging equipment: Shanghai Zhiwei environmental chamber, model EW-EC03PID02-021220.

[0132] PID performance test: The prepared double-glass photovoltaic modules were subjected to an anti-PID performance test under the conditions of 96h-85℃ / 85RH / -1500V;

[0133] PID power test equipment used to test anti-PID attenuation: Nanjing Lixi Te, model LXT-CELL;

[0134] Characteristic vulcanization time Ts1 and Ts2 testing: Using a rotorless vulcanizer, Alpha, MDR; under the conditions of 145°C and 15 min, the characteristic vulcanization time Ts1 and Ts2 of the copolymer were tested.

[0135] Melt index of the copolymer: measured using a melt indexer (CEAST melt indexer, Italy) using the national standard GB / T 3682.1-2018 method. At 190°C and a load of 2.16 kg, the mass of the extrudate was weighed every 6 seconds. This was repeated five times in parallel, and the average value was taken and converted to the mass of the extrudate per 10 minutes, expressed in g / 10 minutes.

[0136] The weight average molecular weight of the copolymer (M w ) and molecular weight distribution (PDI): obtained by high-temperature gel permeation chromatography (GPC, Agilent PL-GPC 220, USA). The sample dissolution temperature was 160°C, the mobile phase was 1,2,4-trichlorobenzene containing 500 ppm BHT (2,6-di-tert-butyl-p-cresol), and the flow rate was 1 mL / min. A K value of 1.016×10 -4 , monodisperse polystyrene standard with α value of 0.7220 (M w The K and α values ​​of the ethylene / α-olefin copolymer (test sample) were 4.416×10 -4and 0.7250.

[0137] Density of the copolymer: measured using a densitometer (METTLER TOLEDO densitometer) according to ASTM-D792.

[0138] Preparation of ethylene / α-olefin copolymers:

[0139] Preparation of Ethylene-Octene Copolymer A: In a 2.0 L continuous process reactor, hexane solvent was injected at a rate of 4.50 kg / h and 1-octene was injected at a rate of 2.91 kg / h. The reactor temperature was controlled at 150° C. Simultaneously, dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (0.35 μmol / min, primary catalyst) and a 10 wt% toluene solution of methylaluminoxane (3.5 μmol / min, co-catalyst) were injected into the reactor. Ethylene was then introduced at a rate of 1.38 kg / h and the reactor was operated continuously under a pressure control of 60 bar. After the operation stabilized (system temperature and pressure were stable), the reaction solution was continuously sampled for approximately 2 hours and the solvent was removed from the reaction solution by evaporation to obtain a polymer product.

[0140] The resulting polymer product was completely dissolved in n-heptane at 80°C with stirring to obtain a polymer solution, wherein the mass ratio of polymer product to solvent was 1:5. After the temperature dropped to room temperature, the polymer solution was added dropwise to ethanol with stirring, wherein the mass ratio of polymer solution to ethanol was 1:1. A precipitate formed during the addition. After the addition was complete, the liquid phase was evaporated to remove the solvent and dried in a vacuum oven at 60°C to constant weight to obtain ethylene-octene copolymer A, with a characteristic relaxation time of 492.2 milliseconds.

[0141] Preparation of Ethylene-Octene Copolymer B: The preparation process was similar to that of Ethylene-Octene Copolymer A, except that the precipitate obtained by dropwise addition of the polymer solution to ethanol was removed and stirred at 80°C until completely dissolved in n-heptane, wherein the mass ratio of the precipitate to n-heptane was 1:6. After the temperature dropped to room temperature, the resulting solution was dropwise added to a mixed solvent of ethanol and methyl hexanophenone in a mass ratio of 6:1 while stirring, wherein the mass ratio of the solution to the mixed solvent was 1:1. After the dropwise addition was completed, the liquid phase was evaporated to remove the solvent, and the polymer was dried in a vacuum oven at 60°C to constant weight to obtain Ethylene-Octene Copolymer B, which had a characteristic relaxation time of 210.3 milliseconds.

[0142] Preparation of Ethylene-Butene Copolymer C: In a 2.0 L continuous process reactor, n-octane solvent was injected at 5.0 kg / h and 1-butene was injected at 2.67 kg / h. The reactor temperature was controlled at 146° C. Simultaneously, disilyl tert-butylamine tetramethylcyclopentadiene titanium dichloride (0.48 μmol / min, primary catalyst) and a 10 wt% toluene solution of methylaluminoxane (48 μmol / min, co-catalyst) were injected into the reactor. Ethylene was then introduced at 1.55 kg / h and the reactor was operated continuously under a controlled pressure of 40 bar. After the operation stabilized (system temperature and pressure were stable), the reaction solution was continuously withdrawn for approximately 2 hours and the solvent was removed by flash evaporation to obtain a polymer product.

[0143] The resulting polymer product was completely dissolved in n-heptane at 100°C with stirring to obtain a polymer solution, wherein the mass ratio of polymer product to solvent was 1:5. After the temperature dropped to room temperature, the polymer solution was added dropwise to ethanol with stirring, wherein the mass ratio of polymer solution to ethanol was 1:1. A precipitate formed during the addition. After the addition was complete, the liquid phase was evaporated to remove the solvent and dried in a vacuum oven at 60°C to constant weight to obtain ethylene-butene copolymer C, with a characteristic relaxation time of 387.5 milliseconds.

[0144] Preparation of Ethylene-Butene Copolymer D: The preparation process is similar to that of Ethylene-Butene Copolymer C, except that the precipitate obtained by dropwise addition of the polymer solution to ethanol is removed and completely dissolved in n-heptane at 120°C with stirring. The mass ratio of the precipitate to the n-heptane is 1:5. After the temperature is lowered to room temperature, the resulting solution is added dropwise to a mixed solvent of ethanol and 3-methyl-2-octanone at a mass ratio of 8:1 while stirring. The mass ratio of the solution to the mixed solvent is 1:2. After the addition is complete, the liquid phase is removed from the solvent and dried in a vacuum oven at 60°C to constant weight to obtain Ethylene-Butene Copolymer D, which has a characteristic relaxation time of 240.4 milliseconds.

[0145] Preparation of Ethylene-Hexene Copolymer E: In a 2-L batch reactor, the temperature was raised to 160°C in an oil bath. A vacuum pump was connected to the reactor piping to remove moisture and oxygen. After 2 hours, the stirring speed was set to 500 rpm, and 800 mL of n-heptane and 300 mL of 1-hexene were added with stirring at 80°C. While stirring, bis(methylcyclopentadienyl)zirconium dichloride (4 μmol) and a 2 mol / L toluene solution of methylaluminoxane (2 mL) were added to the reaction solution. Ethylene was introduced into the reactor until the pressure stabilized at 4 MPa. After 10 minutes of polymerization, the ethylene pressure was released and the solvent was removed by vacuum to obtain a polymer product.

[0146] The resulting polymer product was stirred with n-heptane at 80°C until completely dissolved, with a mass ratio of the polymer product to n-heptane of 1:5. After cooling to room temperature, the resulting polymer solution was added dropwise to ethanol while stirring, with a mass ratio of the polymer solution to ethanol of 1:1. A precipitate formed during the addition. After the addition was complete, the liquid phase was removed from the solvent and dried in a vacuum oven at 60°C to constant weight to produce ethylene-hexene copolymer E, which had a characteristic relaxation time of 320.1 milliseconds.

[0147] Preparation of Ethylene-Hexene Copolymer F: The preparation process is similar to that of Ethylene-Hexene Copolymer E, except that the precipitate obtained by dropwise addition of the polymer solution to ethanol is removed and stirred with n-heptane at 80°C until the precipitate is completely dissolved, wherein the mass ratio of the precipitate to n-heptane is 1:6. After the temperature drops to room temperature, the resulting solution is added dropwise to a mixed solvent of ethanol and 1-phenyl-2,4-pentanedione in a mass ratio of 7:1 while stirring, wherein the mass ratio of the solution to the mixed solvent is 1:1. After the addition is complete, the liquid phase is removed from the solvent and dried in a vacuum oven at 60°C to constant weight to obtain Ethylene-Hexene Copolymer F, which has a characteristic relaxation time of 202.8 milliseconds.

[0148] Preparation of Ethylene-Decene Copolymer G: In a 20 L continuous circulation tubular reactor, toluene solvent was injected at 40 kg / h and 1-decene was injected at 20 kg / h. The reactor temperature was controlled at 126°C. Simultaneously, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride (5.0 μmol / min, primary catalyst) and a 7 wt% Al-modified methylaluminoxane (Nouryon, MMAO-3A) toluene solution (200 μmol / min, co-catalyst) were injected into the reactor. Ethylene was then introduced into the reactor at 18.5 kg / h and the pressure was maintained at 45 bar. After the reactor stabilized (system temperature and pressure were stable), the reaction solution was continuously withdrawn for approximately 0.5 h and the solvent removed by flash evaporation and screw extrusion to obtain the polymer product.

[0149] The resulting polymer product was completely dissolved in n-heptane at 140°C with stirring to obtain a polymer solution, wherein the mass ratio of polymer product to solvent was 1:4. After the temperature dropped to room temperature, the polymer solution was added dropwise to ethanol with stirring, wherein the mass ratio of polymer solution to ethanol was 1:3. A precipitate formed during the addition. After the addition was complete, the liquid phase was removed from the solvent and dried in a vacuum oven at 60°C to constant weight to obtain ethylene-decene copolymer G, with a characteristic relaxation time of 498.8 milliseconds.

[0150] Preparation of Ethylene-Decene Copolymer H: The preparation process was similar to that of Ethylene-Decene Copolymer G, except that the precipitate obtained by dropwise addition of the polymer solution to ethanol was removed and stirred with n-heptane at 80°C until the precipitate was completely dissolved. The mass ratio of the precipitate to n-heptane was 1:4. After the temperature dropped to room temperature, the resulting solution was dropwise added to a mixed solvent of ethanol and bicyclo[3.3.1]nonane-3,7-dione at a mass ratio of 6:1 while stirring. The mass ratio of the dissolved solution to the mixed solvent was 1:1. After the addition was complete, the liquid phase was removed from the solvent and dried in a vacuum oven at 60°C to constant weight to obtain Ethylene-Decene Copolymer H. The characteristic relaxation time was measured to be 287.6 milliseconds.

[0151] Preparation of ethylene-octene copolymer I: prepared according to the method of Comparative Example 6 of patent CN113767118B.

[0152] Preparation of ethylene-hexene copolymer J: prepared according to Example 8 of patent US10975173B2.

[0153] The physical properties of the prepared ethylene / α-olefin copolymer are shown in Table 1.

[0154] Table 1

[0155] Example 1

[0156] To 1000 g of ethylene-octene copolymer A (ethylene / α-olefin copolymer) were added 9 g of tert-butyl peroxy-2-ethylhexyl carbonate, 5 g of triallyl isocyanurate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 1 g of bis[2,4-di-tert-butylphenyl]pentaerythritol diphosphite and 1 g of β-[3,5-di-tert-butyl-4-hydroxyphenyl]propionic acid n-octadecyl ester.

[0157] The raw materials were heated to 50°C and mixed evenly. The extruder parameters were adjusted to the temperature from the feed port to the die head of 80°C, 90°C, 90°C, 90°C, 90°C, 95°C, 95°C, 95°C, the screw speed was 45 rpm, the pulling speed was 0.7 rpm, and the winding speed was 1.3 rpm. After extrusion, film casting, cooling, slitting, and winding, a solar cell encapsulation film with a thickness of 0.6 mm was prepared. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to obtain a double-glass photovoltaic module.

[0158] Example 2

[0159] To 1000 g of ethylene-octene copolymer B (ethylene / α-olefin copolymer) were added 9 g of tert-butyl peroxy-2-ethylhexyl carbonate, 5 g of triallyl isocyanurate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 1 g of bis[2,4-di-tert-butylphenyl]pentaerythritol diphosphite and 1 g of β-[3,5-di-tert-butyl-4-hydroxyphenyl]propionic acid n-octadecyl ester.

[0160] The raw materials were heated to 50°C and mixed evenly. The extruder parameters were adjusted to the temperature from the feed port to the die head of 80°C, 90°C, 90°C, 90°C, 90°C, 95°C, 95°C, 95°C, the screw speed was 45 rpm, the pulling speed was 0.7 rpm, and the winding speed was 1.3 rpm. After extrusion, film casting, cooling, slitting, and winding, a solar cell encapsulation film with a thickness of 0.6 mm was prepared. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to obtain a double-glass photovoltaic module.

[0161] Example 3

[0162] To 1000 g of ethylene-butene copolymer C were added 6 g of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2 g of tert-amyl peroxycarbonate, 4 g of trimethylolpropane triacrylate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1 g of antioxidant 1076 and 1 g of antioxidant 1010.

[0163] The raw materials were heated to 50°C and mixed evenly. The extruder parameters were adjusted to the temperature from the feed port to the die head of 80°C, 90°C, 90°C, 90°C, 90°C, 95°C, 95°C, 95°C, the screw speed was 45 rpm, the pulling speed was 0.7 rpm, and the winding speed was 1.3 rpm. After extrusion, film casting, cooling, slitting, and winding, a solar cell encapsulation film with a thickness of 0.6 mm was prepared. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to obtain a double-glass photovoltaic module.

[0164] Example 4

[0165] To 1000 g of ethylene-butene copolymer D were added 6 g of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2 g of tert-amyl peroxycarbonate, 4 g of trimethylolpropane triacrylate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1 g of antioxidant 1076 and 1 g of antioxidant 1010.

[0166] The raw materials were heated to 50°C and mixed evenly. The extruder parameters were adjusted to the temperature from the feed port to the die head of 80°C, 90°C, 90°C, 90°C, 90°C, 95°C, 95°C, 95°C, the screw speed was 45 rpm, the pulling speed was 0.7 rpm, and the winding speed was 1.3 rpm. After extrusion, film casting, cooling, slitting, and winding, a solar cell encapsulation film with a thickness of 0.6 mm was prepared. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to obtain a double-glass photovoltaic module.

[0167] Example 5

[0168] The same method was used as in Example 1, except that the ethylene / α-olefin copolymer used was 1000 g of ethylene-hexene copolymer E.

[0169] Example 6

[0170] The same method was used as in Example 1, except that the ethylene / α-olefin copolymer used was 1000 g of ethylene-hexene copolymer F.

[0171] Example 7

[0172] The same process was carried out as in Example 3, except that the ethylene / α-olefin copolymer used was 1000 g of ethylene-decene copolymer G.

[0173] Example 8

[0174] The same process was carried out as in Example 3, except that the ethylene / α-olefin copolymer used was 1000 g of ethylene-decene copolymer H.

[0175] Comparative Example 1

[0176] To 1000 g of ethylene-butene copolymer I were added 6 g of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2 g of tert-amyl peroxycarbonate, 4 g of trimethylolpropane triacrylate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1 g of antioxidant 1076 and 1 g of antioxidant 1010.

[0177] The raw materials were heated to 50°C and mixed evenly. The extruder parameters were adjusted to the temperature from the feed port to the die head of 80°C, 90°C, 90°C, 90°C, 90°C, 95°C, 95°C, 95°C, the screw speed was 45 rpm, the pulling speed was 0.7 rpm, and the winding speed was 1.3 rpm. After extrusion, film casting, cooling, slitting, and winding, a solar cell encapsulation film with a thickness of 0.6 mm was prepared. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to obtain a double-glass photovoltaic module.

[0178] Comparative Example 2

[0179] To 1000 g of ethylene-hexene copolymer J were added 6 g of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2 g of tert-amyl peroxycarbonate, 4 g of trimethylolpropane triacrylate, 2 g of γ-methacryloyloxypropyltrimethoxysilane, 1 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1 g of antioxidant 1076 and 1 g of antioxidant 1010.

[0180] The raw materials were heated to 55°C and mixed evenly. The extruder parameters were adjusted to the temperatures from the feed port to the die head of 95°C, 105°C, 105°C, 105°C, 105°C, 105°C, 105°C, 105°C, 105°C, 105°C, 105°C, a screw speed of 42 rpm, a pulling speed of 0.6 rpm, and a winding speed of 1.2 rpm. A solar cell encapsulation film with a thickness of 0.6 mm was prepared through the steps of extrusion, cast film formation, cooling, slitting, and winding. Subsequently, tempered glass, encapsulation film, crystalline silicon cell, encapsulation film, and float glass were placed in order from top to bottom, and laminated in a laminator at 145°C to produce a double-glass photovoltaic module.

[0181] The test results of the embodiments and comparative examples are shown in Table 2.

[0182] Table 2

[0183] The experimental results in Table 2 demonstrate that the ethylene / α-olefin copolymers used in the present invention for solar cell encapsulation films significantly shorten the curing time of the films, while also achieving excellent PID resistance, compared to the ethylene / α-olefin copolymers used in the comparative examples. The ethylene / α-olefin copolymers used in the comparative examples do not simultaneously meet conditions (a)-(c) of the present invention. Consequently, the resulting encapsulation films struggle to achieve both a short curing time and excellent PID resistance, failing to achieve a good balance between the two.

[0184] The present invention provides an ethylene / α-olefin copolymer and a composition thereof for solar cell encapsulation film, wherein the matrix resin has a high characteristic relaxation time, which makes the molecular structure more prone to chain entanglement. When the molecular chain lengths are similar, the degree of chain entanglement of the polymer itself increases, and it is easier to form a body cross-linked structure during the lamination cross-linking reaction, so that the vulcanization cross-linking reaction can be completed faster, shortening the processing time, which is manifested as a decrease in the characteristic vulcanization time Ts1 and Ts2. At the same time, the degree of chain entanglement increases, and the polymer is more likely to form a denser cross-linked structure, thereby enhancing the barrier capacity of the encapsulation film to metal ions, thereby showing the effect of improving the anti-PID effect of the photovoltaic encapsulation film, which is manifested as a decrease in the anti-PID attenuation of the front and back surfaces of the 96h component. The characteristic relaxation time of the matrix resin used in Comparative Example 1 is too small, and the vulcanization performance of the prepared film and the anti-PID effect of the component are significantly poor. However, the matrix resin used in Comparative Example 2 has a characteristic relaxation time that is too long, the particles are generally hard, and the density is too high. If the same temperature conditions as in Example 1 are used during the casting process, it is found that it is difficult to completely plasticize the particles. The temperature needs to be increased to completely plasticize the particles, which will reduce production capacity and is not conducive to subsequent downstream processing. In addition, the particle density is too high, causing the resin particles to be more plastic than elastomer. As a result, during the aging process, it is difficult for the additives to migrate into the interior of the resin particles, making the particle additive absorption effect worse, which is manifested as a serious decrease in vulcanization performance and almost no cross-linking. Furthermore, the particles are generally hard, and the protective effect on the battery cells is weak. The battery cells are prone to cracking during lamination, resulting in a reduction in component yield.

[0185] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to enumerate all possible implementations here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An ethylene / α-olefin copolymer for solar cell encapsulation film, characterized in that: The copolymer satisfies the following conditions (a) to (c): (a) The characteristic relaxation time at 190°C is 200.0–500.0 ms at an angular frequency of 0.1–500 rad / s; (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc; (c) The molecular weight distribution is 1.5-3.

2. The ethylene / α-olefin copolymer according to claim 1, characterized in that The characteristic relaxation time is 350.0-500.0 milliseconds, more preferably 400-500 milliseconds.

3. The ethylene / α-olefin copolymer according to claim 1, characterized in that The copolymer has a melt index of 1 g / 10 min to 50 g / 10 min under the conditions of 190° C. and 2.16 kg load.

4. The ethylene / α-olefin copolymer according to any one of claims 1 to 3, characterized in that The weight average molecular weight is 40000-100000 g / mol.

5. The ethylene / α-olefin copolymer according to any one of claims 1 to 3, characterized in that: The α-olefin includes one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-eicosene.

6. The method for preparing the ethylene / α-olefin copolymer for solar cell encapsulation film according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (S1) polymerizing ethylene and α-olefin to obtain a copolymer product; (S2) post-treating the copolymer product to separate therefrom an ethylene / α-olefin copolymer that satisfies conditions (a) to (c) at the same time: (a) under the condition of angular frequency of 0.1-500 rad / s, the characteristic relaxation time at 190° C. is 200.0-500.0 milliseconds, preferably 350.0-500.0 milliseconds, more preferably 400-500 milliseconds; (b) a weight average molecular weight of 20,000 to 200,000 g / mol and a density of 0.850 g / cc to 0.910 g / cc; (c) The molecular weight distribution is 1.5-3.

7. A solar cell encapsulation film composition, characterized in that: The composition comprises the ethylene / α-olefin copolymer according to any one of claims 1 to 5 or the ethylene / α-olefin copolymer prepared by the preparation method according to claim 6; Preferably, the composition further comprises one or more of a cross-linking agent, a co-cross-linking agent, a coupling agent and an antioxidant.

8. A solar cell encapsulation film, characterized in that: The encapsulation film is prepared by using the composition according to claim 7.

9. The method for preparing the solar cell encapsulation film according to claim 8, characterized in that: The steps include: The components in the composition are mixed and melted, extruded and cast into a film, and then cooled and slit.

10. A solar cell assembly comprising the solar cell encapsulation film according to claim 8.