CROSSLINKABLE POLYOLEFIN COMPOSITION

Abstract

A crosslinkable polyolefin composition includes: a) 60.0 wt. % and 99.0 wt. % of an ethylene alpha-olefin co-polymer; b) 1.0 wt. % and 35.0 wt. % of an ethylene-alpha-olefin-diene terpolymer; c) 0.1 wt. % and 5.0 wt. % of a crosslinking agent; with regard to the total weight of the polyolefin composition. A film includes the polyolefin composition. An encapsulated solar cell is encapsulated by at least two sealing layers each including such a film. In addition, a cured solar cell is obtained by subjecting the encapsulated solar cell under conditions of curing the sealing layers, a photovoltaic module includes the cured solar cell.

Claims

1. A polyolefin composition, comprising: a) 60.0 wt. % and 99.0 wt. % of an ethylene alpha-olefin co-polymer, with regard to the total weight of the polyolefin composition; wherein the ethylene alpha-olefin co-polymer has at least one of: i. a peak melting temperature of 60 C. and 90 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; ii. 20.0 wt. % and 45.0 wt. %, of polymeric units derived from one or more alpha-olefins having 3-12 carbon atoms, with regard to the total weight of the ethylene alpha-olefin co-polymer; or iii. a vinyl unsaturation of 6.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012); b) 1.0 wt. % and 35.0 wt. % of an ethylene-alpha-olefin-diene terpolymer, with regard to the total weight of the polyolefin composition, wherein the ethylene-alpha-olefin-diene terpolymer comprises a total vinyl and vinylidene unsaturation of 20.0 and 100.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012); and c) 0.1 wt. % and 5.0 wt. % of a crosslinking agent, with regard to the total weight of the polyolefin composition.

2. The polyolefin composition according to claim 1, wherein the ethylene alpha-olefin co-polymer has at least one of: a) a melt flow rate (MFR) of 5.0 g/10 min and 25.0 g/10 min, when determined at 190 C. at 2.16 kg load in accordance with ASTM D1238 (2013); and/or b) a density of 850 kg/m.sup.3 and 900 kg/m.sup.3, when determined in accordance with ASTM D792 (2008).

3. The polyolefin composition according to claim 1, wherein the ethylene alpha-olefin co-polymer comprises the ethylene-alpha-olefin-diene terpolymer, and the ethylene-alpha-olefin-diene terpolymer comprises polymeric units derived from (i) ethylene; (ii) one or more alpha-olefins comprising 3-12 carbon atoms; and (iii) a diene selected from the group consisting of 5-ethylidene-2-norbornene, 5-propylidene-5-norbornene, dicyclopentadiene, 5-vinyl-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, norbornadiene, 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 5-methyl-1,5-heptadiene, 6-methyl-1,5-heptadiene, 6-methyl-1,7-octadiene, 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 2,5-norbornadiene and 7-methyl-1,6-octadiene.

4. The polyolefin composition according to claim 1, wherein the crosslinking agent is an organic peroxide selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 3-di-t-butylperoxide, t-dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne, dicumylperoxide, ,-bis(t-butylperoxyisopropyl)benzene, n-butyl-4,4-bis(t-butylperoxy)butane, 2,2-di(tert-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, tertiarybutylperoxy-2-ethylhexyl carbonate, t-butylperoxybenzoate, 1,6-di(t-butylperoxycarbonyloxy)hexane, and combinations thereof.

5. The polyolefin composition according to claim 1, wherein the polyolefin composition, further comprises: a) 0.05 wt. % and 5.0 wt. %, of a coupling agent; and b) 0.05 wt. % and 5.0 wt. % of one or more additives; with regard to the total weight of the polyolefin composition, wherein the one or more additives is selected from anti-oxidants, heat stabilizers, acid scavengers, release agents, plasticizers, hindered amine light stabilizer, antistatic additive, non-phenolic processing stabilizer, lubricants, anti-statics, scratch resistance agents, recycling additives, clarifying agent, processing stabilizers, antimicrobial agents, anti-fogging additives, slip additives, anti-blocking additives, non-phenolic processing stabilizer, or combinations thereof.

6. The polyolefin composition according to claim 5, wherein the composition comprises: a) 60.0 wt. % and 99.0 wt. % of the ethylene alpha-olefin co-polymer; b) 1.0 wt. % and 35.0 wt. % of the ethylene-alpha-olefin-diene terpolymer; c) 0.1 wt. % and 5.0 wt. % of the crosslinking agent; d) 0.05 wt. % and 5.0 wt. %, of the coupling agent; and e) 0.05 wt. % and 5.0 wt. % of one or more additives; with regard to the total weight of the polyolefin composition.

7. The polyolefin composition according to claim 1, wherein the polyolefin composition has at least one of: a) volume resistivity of >1.010.sup.15 .Math.cm, when determined in accordance with ASTM D257-14 (2021) at an applied voltage of 1000V for a time period of 600 seconds and at a temperature of 25 C.; b) a peak melting temperature of 60 C. and 75 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; c) a density of 850 kg/m.sup.3 and 880 kg/m.sup.3, when determined in accordance with ASTM D792 (2008); d) a beta conversion () for crosslinking at 150 C. of 0.4 and 0.7 at a time period of 1000 seconds, wherein the beta conversion for crosslinking is determined by using the formula: Beta conversion ()=(G(1000)G(0))/(G(5000)G(0)), wherein G(1000) is the storage modulus of the polyolefin composition at time 1000 seconds, G(0) is the storage modulus of polyolefin composition at time 0 seconds, G(5000) is the storage modulus of the polyolefin composition at time 5000 seconds, wherein the storage modulus is determined in accordance with ISO 6721-10 at a temperature of 150 C. under a nitrogen environment using a parallel plate set-up at a frequency of 6.28 radian/sec, and at an oscillation strain of 0.1%; e) a tensile modulus of 11.0 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); f) a tensile strength @ break of 10.5 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); or g) a Durometer Hardness (Shore Hardness D) of 19.0, when determined in accordance with ASTM D2240-15 (2021).

8. A process for preparing the polyolefin composition according to claim 1, wherein the process comprises the steps of: a) providing to an extruder a set of ingredients comprising an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, optionally a coupling agent, and optionally one or more additives; and b) extruding the set of ingredients at a melt temperature of 100 C. and forming the composition.

9. A film comprising or consisting of the polyolefin composition according to claim 1.

10. A process for preparing the film of claim 9, wherein the process comprises the steps of: a) providing to an extruder a set of ingredients comprising an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, optionally a coupling agent, and optionally one or more additives; b) extruding the set of ingredients at a melt temperature of 100 C. and forming an extrudate; and c) casting the extrudate at a temperature of 100 C. and forming the film.

11. An encapsulated solar cell comprising a solar cell positioned between a first sealing layer and a second sealing layer, wherein each of the first sealing layer and the second sealing layer comprises the film of claim 9, wherein the solar cell is positioned such that the first sealing layer and the second sealing layer are joined so as to completely encapsulate the solar cell.

12. A cured solar cell obtained by subjecting the encapsulated solar cell of claim 11 under conditions sufficient to cure the first sealing layer and the second sealing layer.

13. A process comprising the steps of: (a) providing the first sealing layer, the second sealing layer, and the solar cell of claim 11; (b) assembling the first sealing layer, the solar cell, and the second sealing layer and forming the encapsulated solar cell; and (c) curing the encapsulated solar cell under conditions sufficient to cure the first sealing layer and the second sealing layer to form the cured solar cell.

14. A photovoltaic module comprising the cured solar cell according to claim 12, wherein the photovoltaic module comprises: a) a front protection member; b) a back protection member; c) the cured solar cell, wherein the cured solar cell is positioned between the front protection member and the back protection member.

15. (canceled)

16. The polyolefin composition of claim 1, wherein the ethylene alpha-olefin co-polymer comprises polymeric units derived from ethylene and one or more alpha-olefin selected from 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, or combinations thereof.

17. The polyolefin composition of claim 16, wherein the alpha-olefin is selected from 1-butene or 1-octene.

18. The polyolefin composition of claim 3, wherein the ethylene-alpha-olefin-diene terpolymer is ethylene/propylene/5-ethylidene-2-norbornene copolymer.

19. The polyolefin composition of claim 4, wherein the crosslinking agent is dicumylperoxide.

Description

DETAILED DESCRIPTION

[0015] Preferably, the invention relates to a polyolefin composition, comprising: [0016] a) 60.0 wt. % and 99.0 wt. % of an ethylene alpha-olefin co-polymer, with regard to the total weight of the polyolefin composition, preferably wherein the ethylene alpha-olefin co-polymer comprises polymeric units derived from ethylene and one or more alpha-olefin selected from 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, or combinations thereof, preferably the alpha-olefin is selected from 1-butene or 1-octene, further wherein the ethylene alpha-olefin co-polymer has at least one of: [0017] i. a peak melting temperature of 60 C. and 90 C., preferably 65 C. and 75 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; [0018] ii. 20.0 wt. % and 45.0 wt. %, preferably 28.0 wt. % and 40.0 wt. %, preferably 30.0 wt. % and 40.0 wt. %, of polymeric units derived from one or more alpha-olefins having 3-12 carbon atoms, with regard to the total weight of the ethylene alpha-olefin co-polymer; [0019] iii. a vinyl unsaturation of 6.0 per 10.sup.5 carbon atoms, preferably 7.0 per 10.sup.5 carbon atoms, preferably 12.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012);

[0020] b) 1.0 wt. % and 35.0 wt. % of an ethylene-alpha-olefin-diene terpolymer, with regard to the total weight of the polyolefin composition, wherein the ethylene-alpha-olefin-diene terpolymer comprises a total vinyl and vinylidene unsaturation of 20.0 and 100.0 per 10.sup.5 carbon atoms, preferably 30.0 and 80.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012); and [0021] c) 0.1 wt. % and 5.0 wt. % of a crosslinking agent, with regard to the total weight of the polyolefin composition.

[0022] The ethylene alpha-olefin co-polymer may be so selected to have a suitable melt flow rate and density. Preferably the ethylene alpha-olefin co-polymer may have at least one of: [0023] a) a melt flow rate (MFR) of 5.0 g/10 min and 25.0 g/10 min, preferably 10.0 g/10 min and 20.0 g/10 min, preferably 11.0 g/10 min and 15.0 g/10 min, when determined at 190 C. at 2.16 kg load in accordance with ASTM D1238 (2013); and/or [0024] b) a density of 850 kg/m.sup.3 and 900 kg/m.sup.3, preferably 870 kg/m.sup.3 and 880 kg/m.sup.3, when determined in accordance with ASTM D792 (2008).

[0025] The ethylene alpha-olefin co-polymer may for example contain a suitable amount of chain end unsaturation expressed as the amount of vinyl unsaturation per 10.sup.5 carbon atoms. Without being bound by any specific theory, it is believed that for the ethylene alpha-olefin co-polymer, the vinyl unsaturation content influences the rate of crosslinking and therefore the amount of vinyl unsaturation content should desirably be present above a certain limit in order to promote crosslinking. On the other hand it is believed that, for the ethylene alpha-olefin co-polymer, the vinylidene unsaturation content has limited influence in promoting crosslinking. Therefore, the type of unsaturation content (e.g. vinyl or vinylidene) will play a role in the selection of a suitable ethylene alpha-olefin co-polymer for improving crosslinking.

[0026] Preferably, the ethylene alpha-olefin co-polymer has a vinyl unsaturation of 6.0 per 10.sup.5 carbon atoms, preferably 7.0 per 10.sup.5 carbon atoms, preferably 12.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012). Preferably, the ethylene alpha-olefin co-polymer has a vinyl unsaturation of 6.0 and 25.0, preferably 10.0 and 20.0 per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012).

[0027] Preferably the ethylene alpha-olefin co-polymer has: [0028] a) a peak melting temperature of 60 C. and 90 C., preferably 65 C. and 75 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; and/or [0029] b) 20.0 wt. % and 45.0 wt. %, preferably 28.0 wt. % and 40.0 wt. %, preferably 30.0 wt. % and 40.0 wt. %, of polymeric units derived from one or more alpha-olefins having 3-12 carbon atoms, with regard to the total weight of the ethylene alpha-olefin co-polymer; and/or [0030] c) a vinyl unsaturation of 6.0 per 10.sup.5 carbon atoms, preferably 7.0 per 10.sup.5 carbon atoms, preferably 12.0 per 10.sup.5 carbon atoms, when determined using in accordance with ASTM D6248-98 (2012); [0031] d) a melt flow rate (MFR) of 5.0 g/10 min and 25.0 g/10 min, preferably 10.0 g/10 min and 20.0 g/10 min, preferably 11.0 g/10 min and 15.0 g/10 min, when determined at 190 C. at 2.16 kg load in accordance with ASTM D1238 (2013); and/or [0032] e) a density of 850 kg/m.sup.3 and 900 kg/m.sup.3, preferably 870 kg/m.sup.3 and 880 kg/m.sup.3, when determined in accordance with ASTM D792 (2008).

[0033] Preferably, the peak melting temperature of the ethylene alpha-olefin co-polymer may be of 70 C. and 75 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle. At this melting temperature, the resultant polyolefin composition may be processed effectively while retaining its thermal and creep stability.

[0034] The ethylene alpha-olefin co-polymer may for example comprise polymeric units derived from ethylene and one or more alpha-olefins selected from 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, or combinations thereof. Preferably, the alpha-olefin is selected from 1-butene or 1-octene. In certain embodiments of the invention, the polymeric units derived from one or more alpha-olefins having 3-12 carbon atoms, may be present in a suitable amount in the ethylene alpha-olefin copolymer in order to impart the desired balance of crystalline and amorphous phase in the copolymer.

[0035] Preferably, the ethylene alpha-olefin co-polymer has 20.0 wt. % and 45.0 wt. %, preferably 28.0 wt. % and 40.0 wt. %, preferably 30.0 wt. % and 40.0 wt. %, preferably 35.0 wt. % and 40.0 wt. %, of polymeric units derived from one or more alpha-olefins having 3-12 carbon atoms, with regard to the total weight of the ethylene alpha-olefin co-polymer. The polymeric units derived from ethylene and the alpha-olefin may for example be determined via 13C NMR spectrometry according to the method presented in JAPS, Vol. 42, pp. 399-408, 1991.

[0036] The polyolefin composition comprises an ethylene-alpha-olefin-diene terpolymer having a certain content of end chain unsaturation expressed as the total amount of vinyl and vinylidene unsaturation per 10.sup.5 carbon atoms. Without being bound by any specific theory, it is believed that the total amount of vinyl and vinylidene unsaturation should be above a certain limit as both vinyl and vinylidene unsaturation contribute to promoting crosslinking reaction in terpolymers. Preferably, the ethylene-alpha-olefin-diene terpolymer comprises a total vinyl and vinylidene unsaturation of 20.0 and 100.0, preferably 30.0 and 80.0, preferably 35.0 and 50.0, per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98 (2012).

[0037] Preferably, the ethylene-alpha-olefin-diene terpolymer comprises a vinylidene unsaturation of 5.0 and 50.0, preferably 25.0 and 50.0, preferably 27.0 and 40.0, per 10.sup.5 carbon atoms, when determined in accordance with ASTM D6248-98. In some preferred embodiments of the invention, the content of unsaturation may be measured by .sup.13C NMR on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe head operating at 125 C., whereby the samples are dissolved at 130 C. in C.sub.2D.sub.2Cl.sub.4 containing DBPC as stabilizer in accordance with ASTM D6248-98 (2012).

[0038] The ethylene-alpha-olefin-diene terpolymer comprises: 1) polymeric units derived from ethylene, 2) polymeric units derived from an alpha-olefin, and 3) polymeric units derived from a diene. For example, the ethylene-alpha-olefin-diene copolymer may comprise polymeric units derived from (i) ethylene; (ii) one or more alpha-olefins comprising 3-12 carbon atoms, preferably the one or more alpha olefin is selected from the group consisting of propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene; and (iii) a diene selected from the group consisting of 5-ethylidene-2-norbornene (ENB), 5-propylidene-5-norbornene, dicyclopentadiene (DCPD), 5-vinyl-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, norbornadiene, 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 5-methyl-1,5-heptadiene, 6-methyl-1,5-heptadiene, 6-methyl-1,7-octadiene, 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 2,5-norbornadiene and 7-methyl-1,6-octadiene. Preferably, the ethylene-alpha-olefin-diene terpolymer is ethylene-propylene-diene terpolymer. Preferably the ethylene-alpha-olefin-diene terpolymer is ethylene/propylene/5-ethylidene-2-norbornene terpolymer.

[0039] The ethylene-alpha-olefin-diene terpolymer has a suitable proportion of polymeric units derived from ethylene, alpha olefin monomers and a diene monomer. The ethylene-alpha-olefin-diene terpolymer may for example comprise: [0040] a) 40.0 and 80.0 wt % of polymeric units derived from ethylene, when determined in accordance with ASTM D3900 (2015); [0041] b) 20.0 and 50.0 wt % of polymeric units derived from alpha-olefin, preferably propylene, when determined in accordance with ASTM D3900 (2015); and [0042] c) 0.1 and 15.0 wt % of polymeric units derived from a diene monomer, preferably the diene monomer is 5-ethylidene-2-norbornene (ENB), when determined in accordance with ASTM D6047 (99),
with regard to the total weight of the ethylene-alpha-olefin-diene terpolymer.

[0043] The ethylene, alpha-olefin and diene monomers content of the terpolymer may for example be determined via .sup.13C NMR spectrometry according to the method presented in JAPS, Vol. 42, pp. 399-408, 1991. The ethylene-alpha-olefin-diene terpolymer may for example have a Mooney viscosity ML (1+4) of 10.0 and 100.0 MU, preferably 20.0 and 80.0 MU, when determined in accordance with ASTM D1646. The ethylene-alpha-olefin-diene terpolymer may for example have a density of 850.0 kg/m.sup.3 and 910.0 kg/m.sup.3, preferably 870.0 kg/m.sup.3 and 900.0 kg/m.sup.3, when determined in accordance with ASTM D297-15 (2019).

[0044] In some embodiments of the invention, the polyolefin composition comprises a crosslinking agent. Preferably, the crosslinking agent is an organic peroxide selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 3-di-t-butylperoxide, t-dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne, dicumylperoxide, ,-bis(t-butylperoxyisopropyl)benzene, 2,2-di(tert-butylperoxy)butane, n-butyl-4,4-bis(t-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, tertiarybutylperoxy-2-ethylhexyl carbonate, t-butylperoxybenzoate, 1,6-di(t-butylperoxycarbonyloxy)hexane, and combinations thereof. Preferably, the crosslinking agent is dicumylperoxide (DCP).

[0045] The crosslinking agent may be selected to have a suitable half-life time intended for use in an encapsulant. For example, if the half-life time of the organic peroxide at a particular temperature is too low, then the composition may be prematurely cross-linked thereby adversely affecting its processability during lamination or molding. On the other hand, if the half-life time of the organic peroxide is high, the overall processing efficiency is reduced during the lamination process or during the photovoltaic module production.

[0046] For example, the crosslinking agent may be an organic peroxide having a half-life time of 3.0 minutes and 85.0 minutes, preferably 10.0 minutes and 70.0 minutes, preferably 12.0 minutes and 25.0 minutes, when measured using the equation t.sub.0.5=ln(2)/k, where t.sub.0.5 is the half life time and k is the reaction rate constant determined using the Arrhenius Equation at a temperature of 140 C.

[0047] Preferably, the polyolefin composition may further comprise: 0.05 wt. % and 5.0 wt. %, of a coupling agent, preferably a silane coupling agent. The amount of silane coupling agent used in the practice of this invention may vary widely depending upon the nature of the ethylene--olefin copolymer, the type of silane used, processing conditions, grafting efficiency, intended application area, and similar such factors, but typically at least 0.05, preferably at least 0.5 wt % is used based on the total weight of the polyolefin composition.

[0048] Preferably, the coupling agent may be grafted to the ethylene alpha-olefin co-polymer. Suitable coupling agents include silane coupling agents. For example, any suitable silane coupling agent that will effectively graft and crosslink the ethylene alpha-olefin co-polymer may be used in the practice of this invention. Suitable silanes coupling agents include unsaturated silanes that comprise an ethylenically unsaturated hydrocarbyl group, such as a vinyl, allyl, isopropenyl, butenyl, cyclohexenyl or -(meth)acryloxy allyl group, and a hydrolyzable group, such as, for example, a hydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group. Non-limiting examples of hydrolyzable or polar groups include methoxy, acrylates, ethoxy, formyloxy, acetoxy, proprionyloxy, and alkyl or arylamino groups. Preferred silane coupling agents are the unsaturated alkoxy silanes, which may be grafted onto the ethylene alpha-olefin co-polymer.

[0049] These silanes and their methods of preparation are described in the patent, U.S. Pat. No. 5,266,627 and incorporated in this disclosure as a reference. Vinyl trimethoxy silane, vinyl triethoxy silane, -(meth)acryloxy propyl trimethoxy silane and mixtures of these silanes, are some of the preferred silane coupling agents suitable for use in accordance with this invention.

[0050] More preferably, the polyolefin composition comprises 0.05 wt. % and 5.0 wt. %, of a silane coupling agent, wherein the silane coupling agent is selected from vinyl trimethoxy silane, vinyl triethoxy silane, -(meth)acryloxy propyl trimethoxy silane, and combinations thereof. Alternatively, the silane coupling agents may be blended with the polyolefin composition and subsequently compounded using an extruder.

[0051] Preferably, the polyolefin composition may further comprise: 0.05 wt. % and 5.0 wt. % of one or more additives; with regard to the total weight of the polyolefin composition. The one or more additives may be selected from anti-oxidants, heat stabilizers, acid scavengers, release agents, plasticizers, hindered amine light stabilizer, antistatic additive, non-phenolic processing stabilizer, lubricants, scratch resistance agents, recycling additives, clarifying agent, processing stabilizers, antimicrobial agents, anti-fogging additives, slip additives, anti-blocking additives, non-phenolic processing stabilizer, or combinations thereof.

[0052] The polyolefin composition may further comprise a non-phenolic processing stabilizer. The non-phenolic processing stabilizer may for example be present in an amount of 0.05 wt. % and 5.0 wt. %, with regard to the total weight of the polyolefin composition. For example, the non-phenolic processing stabilizer comprises a mixture of hydroxylamine and a phosphite compound, preferably a 1:1 mixture of a hydroxylamine and a phosphite compound. Preferably, non-phenolic processing stabilizer is a 1:1 mixture of N,N-dioctadecylhydroxylamine (Irgastab FS042) and a tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168).

[0053] The polyolefin composition may further comprise a hindered amine light stabilizer. Preferably the hindered amine light stabilizer is poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6 hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]) (Chimasorb 944FD or Sabostab UV94/=HALS). The hindered amine light stabilizer may for example be present in an amount of 0.05 wt. % and 5.0 wt. % with regard to the total weight of the polyolefin composition.

[0054] The coupling agent and the one or more additives may be present in a suitable amount such that each of the coupling agent and the one or more additives is present in an amount of 0.05 wt. % and 5.0 wt. %, with regard to the total weight of the polyolefin composition.

[0055] Preferably, the polyolefin composition comprises: [0056] a) 0.05 wt. % and 5.0 wt. %, of a coupling agent; and [0057] b) 0.05 wt. % and 5.0 wt. % of one or more additives;
with regard to the total weight of the polyolefin composition, wherein the one or more additives is selected from anti-oxidants, heat stabilizers, acid scavengers, release agents, plasticizers, hindered amine light stabilizer, antistatic additive, non-phenolic processing stabilizer, lubricants, anti-statics, scratch resistance agents, recycling additives, clarifying agent, processing stabilizers, antimicrobial agents, anti-fogging additives, slip additives, anti-blocking additives, non-phenolic processing stabilizer, or combinations thereof.

[0058] In some preferred embodiments of the invention, the composition comprises: [0059] a) 60.0 wt. % and 99.0 wt. % of the ethylene alpha-olefin co-polymer; [0060] b) 1.0 wt. % and 35.0 wt. % of the ethylene-alpha-olefin-diene terpolymer; [0061] c) 0.1 wt. % and 5.0 wt. % of the crosslinking agent; [0062] d) 0.05 wt. % and 5.0 wt. %, of the coupling agent; and [0063] e) 0.05 wt. % and 5.0 wt. % of one or more additives;
with regard to the total weight of the polyolefin composition.

[0064] Accordingly, the polyolefin composition has a unique set of properties, which render the composition to be useful for use as encapsulants for solar cells and other electronic modules. For example, the polyolefin composition may have has at least one of: [0065] a) volume resistivity (VR) of >1.010.sup.15 .Math.cm, preferably the polyolefin composition has a volume resistivity (VR) of >1.010.sup.15 .Math.cm and <2.010.sup.18 .Math.cm, preferably >1.010.sup.16 .Math.cm and <1.010.sup.17 .Math.cm, when determined in accordance with ASTM D257-14 (2021) at an applied voltage of 1000V for a time period of 600 seconds and at a temperature of 25 C.; [0066] b) a peak melting temperature of 60 C. and 75 C., preferably 65 C. and 72 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; [0067] c) a density of 850 kg/m.sup.3 and 880 kg/m.sup.3, when determined in accordance with ASTM D792 (2008); [0068] d) a beta conversion () for crosslinking of 0.4 and 0.7 at a time period of 1000 seconds, wherein the beta conversion for crosslinking is determined by using the formula: [0069] Beta conversion ()=(G(1000)G(0))/(G(5000)G(0)), wherein G(1000) is the storage modulus of the polyolefin composition at time 1000 seconds, G(0) is the storage modulus of the polyolefin composition at time 0 seconds, G(5000) is the storage modulus of the polyolefin composition at time 5000 seconds, wherein the storage modulus is determined in accordance with ISO 6721-10 at a temperature of 150 C. under a nitrogen environment using a parallel plate set-up at a frequency of 6.28 radian/sec, and at an oscillation strain of 0.1%; [0070] e) a tensile modulus of 11.0 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); [0071] f) a tensile strength @ break of 10.5 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); [0072] g) a Durometer Hardness (Shore Hardness D) of 19.0, when determined in accordance with ASTM D2240-15 (2021).

[0073] Preferably, the polyolefin composition has at least one of: [0074] a) volume resistivity (VR) of >1.010.sup.15 .Math.cm, preferably the polyolefin composition has a volume resistivity (VR) of >1.010.sup.15 .Math.cm and <2.010.sup.18 .Math.cm, preferably >1.010.sup.16 .Math.cm and <1.010.sup.17 .Math.cm, when determined in accordance with ASTM D257-14 (2021) at an applied voltage of 1000V for a time period of 600 seconds and at a temperature of 25 C.; [0075] b) a peak melting temperature of 60 C. and 75 C., preferably 65 C. and 72 C., when determined in accordance with ASTM D3418-15, using Differential Scanning calorimetry (DSC) with a first heating and cooling cycle at a temperature between 23 C. to 200 C. and at a heating and a cooling rate of 10 C./min for a 10 mg film sample, using a nitrogen purge gas at flow rate of 505 mL/min, followed by a second heating cycle identical to the first heating cycle; [0076] c) a density of 850 kg/m.sup.3 and 880 kg/m.sup.3, when determined in accordance with ASTM D792 (2008); [0077] d) a beta conversion () for crosslinking of 0.4 and 0.7 at a time period of 1000 seconds, wherein the beta conversion for crosslinking is determined by using the formula: [0078] Beta conversion ()=(G(1000)G(0))/(G(5000)G(0)), wherein G(1000) is the storage modulus of the polyolefin composition at time 1000 seconds, G(0) is the storage modulus of the polyolefin composition at time 0 seconds, G(5000) is the storage modulus of the polyolefin composition at time 5000 seconds, wherein the storage modulus is determined in accordance with ISO 6721-10 at a temperature of 150 C. under a nitrogen environment using a parallel plate set-up at a frequency of 6.28 radian/sec, and at an oscillation strain of 0.1%; [0079] e) a tensile modulus of 11.0 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); [0080] f) a tensile strength @ break of 10.5 MPa and 25.0 MPa, when determined in accordance with ASTM D882 (2018); [0081] g) a Durometer Hardness (Shore Hardness D) of 19.0, when determined in accordance with ASTM D2240-15 (2021).

[0082] In particular, the polyolefin composition has a suitable curing time, enabling the composition to be cross-linked at a relatively short duration of time. A convenient proxy for determining the ease of cross-linking is by determining the Beta conversion. In other words, beta conversion represents the extent of cross-linking at a particular time period, for example 1000 seconds, after the initiation of the cross-linking reaction. For the purpose of calculation, the time period of 5000 seconds is taken to represent a sufficiently long time period (an infinite time period from the initiation of the process) under which a certain degree of cross-linking reaction, for example >60%, preferably >80%, more preferably >85%, has been achieved. Preferably, the polyolefin composition has a volume resistivity (VR) of >1.010.sup.15 .Math.cm and <2.010.sup.18 .Math.cm, preferably >1.010.sup.16 .Math.cm and <1.010.sup.17 .Math.cm and a beta conversion () for crosslinking at 150 C. of 0.4 and 0.7, at a time period of 1000 seconds, indicating that the polyolefin composition is able to retain high volume resistivity even while having fast cross-linking properties.

[0083] In some preferred embodiments of the invention, the invention is directed to a process for preparing the polyolefin composition, wherein the process comprises the steps of: [0084] a) providing to an extruder a set of ingredients comprising an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, optionally a coupling agent, and optionally one or more additives; and [0085] b) extruding the set of ingredients at a melt temperature of 100 C. and forming the composition.

[0086] Preferably, in some embodiments of the invention, the set of ingredients comprises an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, a silane coupling agent, and one or more additives. Preferably, the ingredients are extruded at a melt temperature of 55 C. and 100 C., preferably at a melt temperature of 60 C. and 80 C., and forming the composition. The ingredients may be dry blended to form a blended mixture outside the extruder and subsequently the blended mixture may be introduced inside the extruder via the hoper of the extruder. Alternatively, the set of ingredients may be introduced individually into the extruder via the hopper such that the ingredients are blended inside the extruder prior to being extruded.

[0087] In some preferred embodiments of the invention, the invention is directed to a film comprising or consisting of the polyolefin composition of the present invention. The film may be prepared by a process, comprising the steps of: [0088] a) providing to an extruder a set of ingredients comprising an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, optionally a coupling agent, and optionally one or more additives; [0089] b) extruding the set of ingredients at a melt temperature of 100 C. and forming an extrudate; [0090] c) casting the extrudate at a temperature of 100 C. and forming the film.

[0091] In some embodiments of the invention, the set of ingredients comprises an ethylene alpha-olefin co-polymer, an ethylene-alpha-olefin-diene terpolymer, a crosslinking agent, a silane coupling agent, and one or more additives. Preferably, during the film production, the ingredients are extruded at a melt temperature of 55 C. and 100 C., preferably at a melt temperature of 60 C. and 80 C., and forming the extrudate. The extrudate may be further casted to form the film. The casting of the film may be carried out at any suitable temperature of 70 C. and 100 C. In some embodiments of the invention, the film so obtained may be further heated and subsequently stretched to form an oriented film, for example a bi-directionally oriented film.

[0092] The film, once formed, may be used for preparing sealing layers suitable to be used in photovoltaic modules or other electronic modules. For example, in some embodiments of the invention, the invention is directed to an encapsulated solar cell comprising a solar cell positioned between a first sealing layer and a second sealing layer, wherein each of the first sealing layer and the second sealing layer comprise or consist of the film of the present invention, wherein the solar cell may be positioned such that the first sealing layer and the second sealing layer are joined so as to completely encapsulate the solar cell. The film may have a suitable thickness. For example, the film has a cross-sectional thickness of 200 m and 800 m, preferably 300 m and 500 m.

[0093] Solar cell used for the context of the present invention are known to a person skilled in the art. For example, the solar cell may be any standard commercially available crystalline or amorphous silicon solar cell or CIGS (copper indium gallium selenide) thin film. The person skilled in the art will know what type of electrical connection to use, for example electrical conductors may be metal strips such as strips comprising copper aluminum and/or silver or, in the alternative, may be metal wires.

[0094] The encapsulated solar cell may be subjected to further processing for example, curing to render the encapsulated solar cell suitable to be used in photovoltaic module. For example, in some embodiments of the invention, the invention is directed to a cured solar cell obtained by subjecting the encapsulated solar cell under conditions sufficient to cure the first sealing layer and the second sealing layer.

[0095] The cured solar cell may be prepared by a process comprising the steps of: [0096] (a) providing the first sealing layer, the second sealing layer, and the solar cell; [0097] (b) assembling the first sealing layer, the solar cell, and the second sealing layer and forming the encapsulated solar cell; [0098] (c) curing the encapsulated solar cell under conditions sufficient to cure the first sealing layer and the second sealing layer to form the cured solar cell.

[0099] The expression curing as used herein means crosslinking the various components of the polyolefin composition under heat or radiation or chemically. Preferably, crosslinking can be effected by any one of a number of different methods as known to the person skilled in the art, e.g., by the use of thermally activated initiators, e.g., peroxides and azo compounds; photoinitiators, e.g., benzophenone; radiation techniques including sunlight, UV light, E-beam and x-ray; silane, e.g., vinyl tri-ethoxy or vinyl tri-methoxy silane; and moisture curing. Preferably the crosslinking is carried out using organic peroxides. The expression cured solar cell as used herein means the solar cell encapsulated in a sealing layer, where the sealing layers have been cured under conditions sufficient to induce crosslinking within the sealing layers.

[0100] Preferably, the curing process is carried out by heating. The curing step under heat may for example be carried out at any temperature of 135 C. and 150 C., preferably 140 C. and 145 C. The curing step may for example be carried out for a time period of 1 hour, preferably 30 minutes, preferably 20 minutes and 3 minutes. Advantageously, sealing layers are composed of a film having a polyethylene composition, which enables curing at a relatively short time period while retaining sufficiently high volume resistivity.

[0101] Accordingly, in some embodiments of the invention, the invention is directed to the use of the polyolefin composition or the film, for the reduction of cross-linking time during the production of a photovoltaic module.

[0102] For example, the cured solar cell once formed may be integrated with various components of a photovoltaic module. Preferably, in some embodiments of the invention, the invention is directed to a photovoltaic module comprising the cured solar cell of the present invention. Preferably such a photovoltaic module may comprise: [0103] a) a front protection member; [0104] b) a back protection member; [0105] c) the cured solar cell, wherein the cured solar cell is positioned between the front protection member and the back protection member.

[0106] Preferably, the invention relates to a photovoltaic module comprising the cured solar cell of the present invention, preferably wherein the photovoltaic module comprises: [0107] a) a front protection member; [0108] b) a back protection member; [0109] c) the cured solar cell, wherein the cured solar cell is positioned between the front protection member and the back protection member.

[0110] The front and the back protection member may be prepared of suitable material, for example polypropylene materials. The photovoltaic module may for example be prepared by positioning the cured solar cell between the front protection member and the back protection member followed by thermal treatment to laminate the cured solar cell between the front protection member and the back protection member.

[0111] Alternatively, the cured solar cell may be produced in-situ during the production of the photovoltaic module itself. For example, in some embodiments of the invention the photovoltaic module is prepared by a process involving: [0112] (a) assembling the front protection member, the first sealing layer, the second sealing layer, the solar cell and the back protection member to form a photovoltaic assembly having i) the encapsulated solar cell comprising the solar cell positioned between the first sealing layer and the second sealing layer, ii) the first sealing layer is in contact with the front protection member; and iii) the second sealing layer is in contact with the back protection layer; [0113] (b) subjecting the photovoltaic assembly under conditions of pressure and heat such that at least part of the sealing layers melt to form a laminated photovoltaic assembly; [0114] (c) subjecting the laminated photovoltaic assembly to conditions of curing to form the photovoltaic module comprising the cured solar cell.

[0115] In some embodiments of the invention, the assembling step involves a specific order of assembling the various components of a photovoltaic module to form the photovoltaic assembly. The steps to prepare such a photovoltaic assembly may involve: [0116] a) providing the back protection member; [0117] b) positioning the second sealing layer on the back protection member such that the second sealing layer is in contact with the back protection member; [0118] c) positioning the solar cell on the second sealing layer such that the second sealing layer is positioned between the solar cell and the back protection member; [0119] d) positioning the first sealing layer on the solar cell such that the solar cell is positioned between the first sealing layer and the second sealing layer; [0120] e) positioning the front protection member on the first sealing layer such that the first sealing layer is positioned between the front protection member and the solar cell; [0121] f) subjecting the above assembly to a further set of processing steps including curing, to form the photovoltaic module.

[0122] Optionally, the laminated assembly post curing may be cooled prior to forming the photovoltaic module. Preferably during the heating step, the assembly is heated to a temperature such that the front protection member and the back protection member do not melt. For example the temperature of this heating step may be so chosen such that the front protection member attains a temperature of at least 5 C. below the melting temperature of the front layer. In practice, the temperature of the heating step is chosen as high as possible to enable a maximum adherence between the sealing layers and the protection layers, while at the same time the temperature, is not too high, so that the front and back layers remain solid.

[0123] Specific examples demonstrating some of the embodiments of the invention are included below. The examples are for illustrative purposes only and are not intended to limit the invention. It should be understood that the embodiments and the aspects disclosed herein are not mutually exclusive and such aspects and embodiments can be combined in any way. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLES

[0124] Purpose: For the purposes of exemplifying the present invention, four inventive formulations (IE1-IE3) were prepared and its properties were compared with that of comparative formulations (CE1). The details of the formulations are provided below:

TABLE-US-00001 TABLE 1 Grade Name IE1 IE2 IE3 CE1 Ethylene alpha- C13075DP 94.0 wt. % 89.0 wt. % 79 wt. % 99 wt. % olefin co-polymer (SABIC) (POE) wt. % Ethylene-alpha- NORDEL IP 5.0 wt. % 10.0 wt. % 20 wt. % 0 wt. % olefin-diene 3720P terpolymer (EPDM) wt. % Crosslinking Luperox 1.0 wt. % 1.0 wt. % 1.0 wt. % 1.0 wt. % agent: DCP Dicumylperoxide wt. %

[0125] Method of preparation: The above formulations of weight (50 g) were prepared by dry blending C13075DP, EPDM 3720 and peroxide DCP in a twin screw extruder. The blend was subsequently extruded below 100 C. at a 15 kg/h output to obtain the samples. The samples obtained were further casted at single screw line at 90 C. to make an encapsulant sheet with a thickness of 400 m. The samples obtained were further subjected to a cross-linking or curing condition at 150 C.

[0126] Testing: For measuring beta conversion, the storage modulus was determined in accordance with ISO 6721-10. Rheology measurements were carried out using an ARES-G2 rheometer using 25 mm parallel plates at temperatures of 150 C. The frequency sweep was carried out at a frequency of 6.28 radian/sec and at an oscillation strain of 0.1%. For determining beta conversion, the storage modulus across a time period post the initiation of cross-linking was determined at a time period ranging from zero seconds to 5000 seconds.

[0127] The volume resistivity may be determined in accordance with ASTM D257-14 (2021), at an applied voltage of 1000V for a time period of 600 seconds and at a temperature of 25 C.

[0128] The results from the test analysis are provided below.

TABLE-US-00002 TABLE 2 100% IE1 IE2 IE3 CE1 EPDM Beta conversion 0.406 0.431 0.455 0.385 at 1000 seconds measured at 150 C. Volume resistivity 2.1 1.6 8.5 3.9 1.4 .Math. cm 10.sup.16 10.sup.16 10.sup.15 10.sup.16 10.sup.15

[0129] From the data provided in Table 2, it is evident that with increase in EPDM concentration present in the inventive polyolefin composition (IE1-IE3), the cross-linking time is reduced as indicated by the higher beta conversion value (e.g. IE3 versus CE3). Advantageously the inventive polyolefin compositions are able to retain sufficiently high volume resistivity, rendering such compositions to be suitable for application in the manufacture of photovoltaic modules.