Curable compositions comprising an ethylene polymer, a monoperoxycarbonate, and a tertiary alkyl hydroperoxide

Abstract

The invention relates to a curable composition comprising (a) at least one ethylene polymer, (b) less than 2 parts by weight of at least one monoperoxycarbonate per 100 parts by weight of component (a), (c) 0.4 to less than 4 parts by weight of at least one tertiary alkyl hydroperoxide per 100 parts by weight of component (b). The invention further relates to a method for preventing scorching of a curable composition comprising an ethylene polymer by adding a specific amount of a tertiary alkyl hydroperoxide to the curable composition and a method for preparing a scorch resistant material.

Description

[0001] This application is a divisional application of application number 201780054981.X, which was filed on September 8, 2017.

[0002] This invention relates to curable compositions comprising ethylene polymers, such as ethylene / vinyl acetate copolymers. The invention also relates to methods for preventing scorching of curable compositions comprising such ethylene polymers.

[0003] Ethylene / vinyl acetate (EVA) is a copolymer that is particularly widely used in solar panels as an encapsulation material to protect solar cells (especially the semiconductors they contain) from outdoor environmental factors, particularly moisture and UV radiation, and to provide electrical insulation. EVA does offer good transparency and adhesion to the substrate of photovoltaic (PV) modules, as well as high resistivity and good moisture resistance. These properties can also be used alternatively in the manufacture of laminated glass.

[0004] A common practice is to crosslink these EVA copolymers to improve their thermal stability, particularly their creep strength, their adhesion to substrates, and their resistance to weathering degradation. To this end, a wide variety of crosslinking agents have been used in EVA formulations, typically peroxides such as dicumyl peroxide (DCP), peroxide esters, peroxide ketals, peroxide carbonates, and mixtures thereof. An example of a monoperoxide carbonate used for this purpose is OO-tert-butyl-O-2-ethylhexyl-monoperoxide carbonate (TBEC). This peroxide has been shown to require operating temperatures below those of DCP without imparting a pale yellow hue to the resulting product. Therefore, it is used in the manufacture of photovoltaic modules (see, for example, K. Thaworn et al., Open Journal of Polymer Chemistry, 2012, 2, 77-85). The applicant has further demonstrated that the addition of OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate (TAEC) to TBEC shortens the reaction time and improves the crosslinking density of EVA, thereby increasing the tensile strength of products made from the crosslinked EVA and producing a high modulus (WO 2010 / 007315).

[0005] In the lamination process of PV modules, EVA composition is first deposited on the front plate, then covered with solar cells and deposited on top of them again, and then a back plate is applied to obtain a PV module. The PV module is then heated at a certain high temperature for a period of time and pressed into place, thereby curing the EVA composition.

[0006] It has been found that EVA compositions are prone to premature crosslinking in the barrel or die of the extruder processing them before forming the aforementioned laminates. This phenomenon, known as “scorching,” results in irregularities in the resulting EVA sheets, which in turn impairs the appearance and properties of the PV modules. In some cases, pressure may also build up in the extruder, requiring an interruption of the extrusion process. This is particularly evident in EVAs with relatively low melt flow indices and / or relatively narrow molecular weight distributions (Source: US-4,015,058). However, on the other hand, to achieve commercially viable processing speeds, crosslinking must proceed as quickly as possible once the EVA sheets have been formed and subsequently heated above the thermal decomposition temperature of the peroxides to improve the economics of the process and minimize potential side reactions.

[0007] The same premature crosslinking phenomenon has also been observed in polyolefin elastomers (POEs) that can be used as alternatives to EVA.

[0008] Various solutions have been proposed to prevent scorching of EVA compositions. For example, the addition of polymerization inhibitors to the EVA composition has been suggested. However, undesirable yellowing has been observed. Alternatively, US-4,015,058 proposes the addition of at least 1 wt.% of cumene hydroperoxide and / or tert-butyl hydroperoxide to dicumyl peroxide (DCP). However, due to the presence of DCP, the crosslinking rate obtained using this system is not high enough for industrial applications, particularly in PV module manufacturing. The yellowing problem also persists due to the aromatic structure of DCP.

[0009] Another solution is provided in JP2011-140588, which is said to be suitable for manufacturing PV modules. It involves adding 4-50 parts by weight of hydroperoxide (e.g., tert-butyl hydroperoxide) to 100 parts by weight of an organic peroxide selected from monoperoxycarbonate, dialkyl peroxide, peroxyketal, and peroxy ester. While this solution overcomes the disadvantages associated with the use of DCP, it has been found in JP2011-140588 that the aforementioned amount of hydroperoxide negatively affects the EVA crosslinking density. In this regard, the document recommends increasing the total amount of monoperoxycarbonate and hydroperoxide while maintaining a constant ratio of hydroperoxide to monoperoxycarbonate, approximately 20% (see Table 1).

[0010] Surprisingly, the inventors have discovered that a specific weight ratio of hydroperoxide to monoperoxycarbonate (i.e., 0.4% to less than 4%) can improve the crosslinking density of EVA or POE. Furthermore, the inventors found that at these low weight ratios, the anti-scorching effect of hydroperoxide is significantly increased, contrary to what was expected in JP2011-140588, where even a small amount of crosslinking agent does not impair the rate of the crosslinking reaction. In addition, satisfactory film uniformity was observed, with virtually no bubbles. In this respect, it should be noted that at extrusion temperatures above 100°C, bubbles formed by the evaporation of water entrained within the film are a cause of surface defects that negatively affect the film's resistivity. This is particularly detrimental when the film is used as an encapsulation material in PV modules.

[0011] Therefore, compositions containing ethylene polymers (e.g., EVA) and the aforementioned peroxides can be processed in extrusion units at high production rates without scorching.

[0012] It should be noted that monoperoxycarbonate can also be used to crosslink other ethylene polymers, such as polyolefin elastomers, including polydiene elastomers, including ethylene-propylene-diene (EPDM) elastomers, and polyethylene, including low-density polyethylene and high-density polyethylene, which are particularly used in the manufacture of wire and cable insulation, pipes and hoses (including, for example, pipes for automotive radiators, drinking water, and underfloor heating), roller covers, rotationally molded articles, and foamed articles. Therefore, the compositions of the present invention can also be used in these applications, for example, to prevent scorching while extruding the composition as an insulating sheath onto an electrical conductor.

[0013] More specifically, the present invention relates to a curable composition comprising:

[0014] (a) at least one ethylene polymer,

[0015] (b) Less than 2 parts by weight of at least one monoperoxycarbonate for 100 parts by weight of component (a),

[0016] (c) 0.4 to less than 4 parts by weight of at least one tertiary alkyl hydrogen peroxide for 100 parts by weight of component (b).

[0017] The ethylene polymer used as component (a) of the present invention may be an ethylene homopolymer, or preferably an ethylene copolymer. Examples of ethylene copolymers are those made from ethylene monomers and at least one hydrocarbon selected from those having at least one degree of unsaturation, such as methylene, propylene, butene, pentene, hexene, hepten, octene, butadiene, isoprene, and styrene; acryloyl monomers, such as acrylic acid, methacrylic acid, alkyl methacrylate, and alkyl acrylate, wherein the alkyl group may be selected from, for example, methyl, ethyl, propyl, or butyl; and vinyl monomers, such as vinyl acetate, and other monomers. Typically, these copolymers contain at least 30% by weight of ethylene and at most 70% by weight of one or more other monomers.

[0018] According to a preferred embodiment, the ethylene copolymer is an ethylene / vinyl acetate (EVA) copolymer. The EVA copolymer may contain 15-60 wt.%, preferably 25-45 wt.%, of vinyl acetate (VA) monomer. Examples of such EVA copolymers can be found from ARKEMA under the trade name " 18-150 and " 40-55” obtained.

[0019] Other ethylene polymers that can be used in this invention have been disclosed, for example, in EP 2 242 647. These comprise functionalized polyolefins, such as homopolymers of ethylene or copolymers of ethylene with alkyl (meth)acrylates or vinyl acetate, which can be functionalized by grafting or copolymerizing with maleic anhydride or glycidyl methacrylate. The functionalized polyolefin may optionally be blended with copolymers of ethylene / vinyl carboxylate (e.g., EVA).

[0020] In a preferred embodiment, the ethylene polymer of the present invention is a polyolefin elastomer.

[0021] "Polyolefin" is a polymer derived from olefins, such as ethylene, propylene, butene, hexene, octene, etc. In the context of this definition, "derived from" means that the units in the polymer backbone and / or polymer branches are the result of polymerization or copolymerization of the monomers used to prepare the polymer. Preferably, the polyolefin is a polyolefin elastomer.

[0022] "Polyolefin elastomer" (POE) and similar terms refer to elastomer polymers derived from olefins such as ethylene, propylene, butene, hexene, octene, etc.

[0023] "Elastomer" refers to a polymer that can withstand uniaxial deformation at ambient temperature, preferably at least 20% for 15 minutes, and recover its initial size once the stress is removed, preferably with the remaining deformation less than 5% of its initial size.

[0024] Preferably, based on the weight of the polymer, the α-olefin content of the polyolefin elastomer is at least 15 wt%, preferably at least 20 wt%, and even more preferably at least 25 wt%.

[0025] Preferably, based on the weight of the polymer, the α-olefin content of the polyolefin elastomer is less than 50 wt%, more preferably less than 45 wt%, more preferably less than 40 wt%, and even more preferably less than 35 wt%.

[0026] It can be done 13 2C nuclear magnetic resonance (NMR) spectroscopy was used to measure α-olefin content using the procedure described in Randall (Rev. Macromol Chem. Phys., C29 (2 and 3)).

[0027] α-olefins are preferably C 3-20 Straight-chain, branched, or cyclic α-olefins.

[0028] C 3-20 Examples of α-olefins include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. The α-olefins may also contain cyclic structures, such as cyclohexane or cyclopentane, to obtain α-olefins such as 3-cyclohexyl-1-propylene (allylcyclohexane) and vinylcyclohexane.

[0029] Some cyclic olefins, such as norbornene and related olefins, are considered α-olefins in this invention and can be used to replace some or all of the aforementioned α-olefins.

[0030] Examples of polyolefin elastomers include ethylene / propylene, ethylene / 1-butene, ethylene / 1-hexene, and especially very low-density polyethylene (VLDPE) (e.g., produced by Dow Chemical Company). Ethylene / 1-hexene polyethylene), ethylene / 1-octene, ethylene / styrene, ethylene / propylene / 1-octene, ethylene / propylene / 1-butene, ethylene / 1-butene / 1-octene and ethylene / 1-butene / styrene.

[0031] More preferred polyolefin copolymers are uniformly branched linear and substantially linear ethylene copolymers. Substantially linear ethylene copolymers are particularly preferred and are described more fully in U.S. Patents 5,272,236, 5,278,272, and 5,986,028.

[0032] Specific examples of uniformly branched linear ethylene / α-olefin copolymers can be cited from Mitsui Petrochemicals Company Limited. From Exxon Chemical Company From Dow Chemical Company and

[0033] The polyolefin elastomers of the present invention also include copolymers based on propylene, 1-butene, and other olefins, such as copolymers comprising units largely derived from propylene and a small portion derived from another α-olefin (including ethylene). Exemplary polypropylenes that can be used in the practice of the present invention include those available from Dow Chemical Company. Polymers and available from ExxonMobil Chemical Company polymer.

[0034] Preferably, the polyolefin elastomer of the present invention has a glass transition temperature (Tg) of less than -35°C, preferably less than -40°C, more preferably less than -45°C, and even more preferably less than -50°C, as measured by differential scanning calorimetry (DSC) using the procedure of ASTM D-3418-03.

[0035] Preferably, the polyolefin elastomer of the present invention has a melt index (MI measured by the procedure of ASTM D-1238 (190°C / 2.16kg) of less than 100 g / 10 min, preferably less than 75 g / 10 min, more preferably less than 50 g / 10 min, and even more preferably less than 35 g / 10 min.

[0036] Preferably, the polyolefin elastomer of the present invention has a melt index of at least 1 g / 10 min, more preferably at least 5 g / 10 min.

[0037] Preferably, the polyolefin elastomer of the present invention has a density of less than 0.90 g / cc, more preferably less than 0.89 g / cc, more preferably less than 0.885 g / cc, even more preferably less than 0.88 g / cc, and even more preferably less than 0.875 g / cc.

[0038] Preferably, the polyolefin elastomer of the present invention has a density greater than 0.85 g / cc, more preferably greater than 0.86 g / cc.

[0039] The density is preferably measured using the procedure of ASTM D-792.

[0040] The ethylene polymer is mixed with at least one monoperoxide carbonate. The peroxide compound can be an OO-tert-alkyl-O-alkyl monoperoxide carbonate, preferably selected from: OO-tert-butyl-O-2-ethylhexyl monoperoxide carbonate (TBEC), OO-tert-butyl-O-2-isopropyl-monoperoxide carbonate (TBIC), OO-tert-pentyl-O-2-ethylhexyl-monoperoxide carbonate (TAEC), OO-tert-pentyl-O-2-isopropyl-monoperoxide carbonate (TAIC), and mixtures thereof. These monoperoxide carbonates can be produced by ARKEMA under the trade name... or supply.

[0041] Preferred monoperoxycarbonates are TAEC and TBEC, mixtures thereof, and mixtures of TAEC and TAIC. More preferred monoperoxycarbonates are TAEC and TBEC. According to one embodiment of the invention, a mixture of TBEC and TAEC is used as component (b).

[0042] Preferably, when using a mixture of O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) and O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC), the mass ratio of O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) to O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC) is 0.1:99.9 to 60:40, more preferably 1:99 to 50:50, even more preferably 10:90 to 30:70, even more preferably 15:85 to 25:75, and even more preferably about 20:80.

[0043] Alternatively, the ratio is approximately 50:50.

[0044] Preferably, when using a mixture of O,O-tert-amyl-O-2-isopropyl-monoperoxycarbonate (TAIC) and O,O-tert-amyl-O-(2-ethylhexyl)monoperoxycarbonate (TAEC), the mass ratio of O,O-tert-amyl-O-2-isopropyl-monoperoxycarbonate (TAIC) to O,O-tert-amyl-O-(2-ethylhexyl)monoperoxycarbonate (TAEC) is 20:80 to 99:1, more preferably 30:70 to 80:20, even more preferably 50:50 to 70:30, even more preferably 55:45 to 65:35, and even more preferably about 60:40.

[0045] Alternatively, the ratio is approximately 50:50.

[0046] Preferably, for 100 parts by weight of component (a), the amount of component (b) in the composition of the present invention can be from 0.1 to less than 2 parts by weight, preferably 0.2-1.5 parts by weight, more preferably 0.3-1 parts by weight, more preferably 0.4-1 parts by weight, more preferably 0.4-0.7 parts by weight, and even more preferably about 0.5 parts by weight.

[0047] The third component (c) of the composition according to the invention is tert-alkyl hydrogen peroxide, which may be selected from tert-butyl hydrogen peroxide (TBHP), tert-amyl hydrogen peroxide (TAHP), tert-hexyl hydrogen peroxide (THHP), 1,1,3,3-tetramethylbutyl hydrogen peroxide (TOHP), and p-butylhydrogen peroxide. Alkyl hydroperoxide (PMHP), 2,5-dimethyl-2,5-di-hydroperoxide (2,5-2,5), and mixtures thereof. Preferably, the tertiary alkyl hydroperoxide is TAHP.

[0048] For 100 parts by weight of component (b), the amount of component (c) in the composition of the present invention is preferably 0.4 to less than 4 parts by weight, preferably 0.5 to 3.5 parts by weight, preferably 0.5 to 3 parts by weight, more preferably 0.5 to 2 parts by weight, and even more preferably about 1 part by weight of at least one tertiary alkyl hydrogen peroxide.

[0049] The compositions of the present invention may further comprise a non-organic peroxide crosslinking agent.

[0050] Advantageously, the crosslinking aid has at least one urethane group, maleimide group, acrylate group, methacrylate group, or allyl functional group. Allyl carboxylate can be used, selected from allyl esters, diallyl esters, and triallyl esters.

[0051] The crosslinking aid may be selected from: divinylbenzene, diisopropylbenzene, α-methylstyrene, α-methylstyrene dimer, ethylene glycol dimethacrylate, phenylene dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol 200 dimethacrylate, polyethylene glycol 400 dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate, 1,3-glycerol dimethacrylate, dicarboxylate dimethacrylate, trimethylolpropane trimethacrylate, bisphenol A epoxy diacrylate, and dipropylene glycol diacrylate. Tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycol ethoxylated diacrylate, butanediol diacrylate, hexanediol diacrylate, aliphatic carbamate diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylated triacrylate, trimethylolpropane propoxylated triacrylate, glycerol propoxylated triacrylate, aliphatic carbamate triacrylate, trimethylolpropane triacrylate and dipentaerythritol pentaacrylate, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), N,N′-m-phenylene dimaleimide, butadiene, chloroprene and isoprene.

[0052] More preferably, the crosslinking aid is selected from: triallyl cyanurate, triallyl isocyanurate, N,N′-m-phenylene dimaleimide, triallyl trimellitate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate, and more preferably from: triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethylolpropane triacrylate (TMPTA), and trimethylolpropane trimethacrylate (TMPTMA), and even more preferably trimethylolpropane triacrylate (TMPTA).

[0053] The crosslinking aid may comprise 0.05% to 30% by weight, preferably 0.1% to 10% by weight, relative to the total weight of the composition.

[0054] The primary purpose of using a crosslinking aid in the compositions of this invention is to increase the level of crosslinking. This crosslinking aid can also reduce residual gas emissions during these same peroxide decomposition processes and ultimately reduce the number of air bubbles in the encapsulation film.

[0055] Preferably, the mass ratio of organic peroxide to crosslinking aid is 1:10 to 10:1, and most preferably 1:3 to 3:1.

[0056] The compositions of the present invention may further comprise additives, such as coupling agents, UV stabilizers, UV absorbers, fillers, plasticizers, flame retardants, antioxidants, dyes, and mixtures thereof. Examples of coupling agents are monoalkyl titanates, (vinyl)trichlorosilanes, and (vinyl)trialkoxysilanes. They may comprise 0.01-5 wt.% relative to the weight of the ethylene polymer. UV stabilizers may be selected from hindered amine light stabilizers (HALS), while UV absorbers may be selected from, for example, benzophenones, triazines, and benzotriazoles. These compounds may comprise 0.01-3 wt.% relative to the weight of the ethylene polymer. Inorganic fillers, such as silica, alumina, talc, and calcium carbonate, may be added to improve mechanical strength, but nanoclays are preferred because they provide transparency. Examples of plasticizers are alkyl or aromatic mineral oils, phthalates, azelaic esters, adipates, etc. Antioxidants may be phenols, phosphate esters, or sulfur antioxidants. Alternatively, quinolines such as 1,2-dihydro-2,2,4-trimethylquinoline can be used as antioxidants.

[0057] According to a preferred embodiment, the composition of the present invention does not contain any aromatic peroxides, such as dicumyl peroxide.

[0058] According to a preferred embodiment, the compositions of the present invention do not contain any other peroxides other than the at least one monoperoxycarbonate (b) and the at least one tertiary alkyl hydrogen peroxide (c).

[0059] According to a preferred embodiment, the total amount of peroxide in the composition is less than 2 parts by weight for 100 parts by weight of component (a), more preferably less than 1.5 parts by weight for 100 parts by weight of component (a).

[0060] More preferably, the composition comprises the above-described components (a), (b), and (c) and optionally at least one of the following additives: coupling agent, UV stabilizer, UV absorber, filler, plasticizer, flame retardant, antioxidant, dye, crosslinking aid, and mixtures thereof.

[0061] According to another aspect, this disclosure relates to a method for preparing a composition as defined above, the method comprising the step of mixing components (a), (b), and (c) described above. Advantageously, this step is carried out in conventional equipment such as a continuous mixer and a compounding extruder, preferably at a temperature below the degradation temperature of the peroxide of the present invention.

[0062] The present invention also relates to the use of tertiary alkyl hydrogen peroxide for preventing scorching of a curable composition comprising (a) at least one ethylene polymer and (b) at least one monoperoxycarbonate, wherein the tertiary alkyl hydrogen peroxide accounts for 0.4 to less than 4 parts by weight, preferably 0.5 to 3.5 parts by weight, more preferably 0.5 to 3 parts by weight, more preferably 0.5 to 2 parts by weight, and even more preferably about 1 part by weight of component (c) for 100 parts by weight of component (b).

[0063] The present invention also relates to a method for preventing scorching of a curable composition comprising (a) at least one ethylene polymer and (b) at least one monoperoxycarbonate, the method comprising adding at least one tertiary alkyl hydrogen peroxide to the composition in an amount of 0.4 to less than 4 parts by weight relative to 100 parts by weight of component (b), preferably 0.5 to 3.5 parts by weight, more preferably 0.5 to 3 parts by weight, more preferably 0.5 to 2 parts by weight, and even more preferably about 1 part by weight of the at least one tertiary alkyl hydrogen peroxide.

[0064] On the other hand, the present invention relates to a method for preparing scorch-resistant materials comprising ethylene polymers, particularly a method for preparing scorch-resistant materials selected from: encapsulation materials or sealants, particularly solar cell encapsulation materials or sealants, wire and cable insulations, pipes and hoses (including, for example, pipes for automotive radiators, drinking water and underfloor heating), roller covers, rotational molding articles and foamed articles, said method comprising step a) of curing the composition as described above. Preferably, the product is a solar cell encapsulation material or sealant.

[0065] Preferably, the curing step a) includes a lamination step.

[0066] Preferably, step a) is carried out at a temperature of 130-180°C, more preferably 140-165°C.

[0067] Preferably, step a) lasts for 4-30 minutes, more preferably 6-25 minutes.

[0068] Alternatively, step a) may last for 8-30 minutes, more preferably 6-25 minutes.

[0069] Preferably, the method includes a prior and / or concurrent step a′ selected from molding, extruding, and injection of the composition as described above. When the product is a solar cell encapsulation material or sealant, the step is preferably an extrusion step.

[0070] Step a′) can be performed to obtain a sheet with a thickness of, for example, 50-2000 μm, preferably 100-1000 μm.

[0071] Step a′) can be performed using a T-die extruder or a twin-screw extruder connected to a twin-roll mill.

[0072] Preferably, step a′) is performed at a temperature of 80-150°C, more preferably at 90-120°C.

[0073] Preferably, crosslinking is not achieved during step a′).

[0074] In one specific implementation, steps a′) and a) are performed in a single step.

[0075] According to another embodiment, the present invention relates to a method for manufacturing a photovoltaic module, the method comprising the step of pressing a laminate, the laminate comprising, in sequence:

[0076] - Front panel (e.g., glass or PMMA panel),

[0077] - Sheets comprising the compositions of the present invention,

[0078] - At least one solar cell (preferably made of crystalline silicon or organic photovoltaic cells),

[0079] - Another sheet comprising the composition of the present invention, and

[0080] - Backing sheet (e.g., multilayer PVDF / PET film, glass plate, or PMMA plate).

[0081] The laminate can then be pressed using conventional techniques under heating and / or vacuum, for example, at a temperature of 130-180°C, more preferably 140-165°C under vacuum, for a curing time of 4-30 minutes, for example 6-25 minutes. Alternatively, step a) may continue for 8-30 minutes, more preferably 6-25 minutes. During this subsequent pressing step, the composition of the invention may crosslink. Preferably, the method comprises a single simultaneous pressing and curing step.

[0082] On the other hand, the present invention relates to scorch-resistant materials comprising ethylene polymers that can be obtained by the methods described above.

[0083] Preferably, the scorch-resistant material containing ethylene polymer is selected from: encapsulation materials or sealants, particularly solar cell encapsulation materials or sealants, wire and cable insulation, pipes and hoses (including, for example, pipes for automotive radiators, drinking water, and underfloor heating), roller covers, rotational molding articles, and foamed articles.

[0084] More preferably, the scorch-resistant material containing ethylene polymer is a film, preferably an EVA film, more preferably an encapsulation material or sealant, and even more preferably a solar cell encapsulation material or sealant.

[0085] The scorch-resistant material comprising ethylene polymer of the present invention exhibits improved crosslinking density of the ethylene polymer, accompanied by a significant reduction in scorch problems (if present). Therefore, it is possible to obtain a film without surface defects and with good resistivity.

[0086] According to another aspect, the present invention relates to a photovoltaic module comprising the scorch-resistant material as described above, preferably a solar cell encapsulation material.

[0087] The invention will be better understood from the following embodiments, which are for illustrative purposes only and are not intended to limit the scope of the invention, which is defined by the appended claims. Example

[0088] Example 1: Anti-scorching effect

[0089] The composition according to the invention is prepared by the following steps: ethylene / vinyl acetate (EVA) copolymer (containing 28% VA) is stirred in a Haake internal mixer at a stirring rate of 50 rpm / min and at 35°C. EVA KA-40 (provided by SUMITOMO) and OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate ( TAEC (obtained from Arkema) and tert-amyl hydrogen peroxide ( TAHP (obtained from Arkema) was mixed for 12 minutes. The polymer mixture was then passed through a two-roll mill set at 60°C to produce sheets approximately 2 mm thick.

[0090] Approximately 2-3 g of the above composition was deposited onto a plate on a moving die rheometer (MDR) provided by GOTECH. The MDR is capable of measuring the curing properties of the sample and includes software for analyzing the results. Each sample was placed in a temperature-controlled chamber between two dies, where the lower die oscillated to apply cyclic stress or strain to the sample, while the upper die was connected to a torque sensor to measure the torque response of the sample during deformation. Stiffness was continuously recorded over time. As curing progressed, the stiffness of the sample increased.

[0091] This device is particularly capable of providing calculated values ​​for ML (minimum torque), MH (maximum torque), tcl0 (time to cure to 10%), and tc90 (time to cure to 90%) as defined by international standards (ASTM D5289 and ISO 6502).

[0092] MDR was operated at 115°C and 145°C, with an oscillation amplitude (deformation degree) of 0.5°, and applied to the sample for 30 minutes. The scorch time was defined as the time required to reach 10% of the total curing, i.e., tcl0.

[0093] The experiment was conducted on the following samples, where the amount of monoperoxycarbonate is expressed as parts per 100 parts of EVA resin (phr), and the amount of TAHP is expressed as parts by weight for 100 parts by weight of monoperoxycarbonate:

[0094]

[0095]

[0096] Table 1.

[0097] As can be seen from the table, TAHP acts as an anti-scorching agent because the scorching time (tcl0) increases with increasing TAHP content. When the TAHP content is below 0.4 wt% relative to TAEC, crosslinking begins even at 115°C (see MH values), which is undesirable. However, when the TAHP content reaches 4 wt% relative to TAEC, the crosslinking time (tc90) increases significantly, resulting in a lower crosslinking rate and lower crosslinking density (MH). At TAHP content below 4 wt% relative to TAEC, scorching is effectively prevented while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0098] Example 2:

[0099] This experiment was conducted under the same conditions as in Example 1, except that a mixture of 20% O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) and 80% O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC) was used instead of TAEC alone. The results are shown in Table 2 below:

[0100]

[0101]

[0102] Table 2.

[0103] In the aforementioned embodiments, when TAHP reaches 4 wt% relative to TAEC+TBEC, the crosslinking time (tc90) increases significantly.

[0104] Example 3:

[0105] This experiment was conducted under the same conditions as in Example 1, except that a mixture of 50% O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) and 50% O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC) was used instead of TAEC alone. The results are shown in Table 3 below:

[0106]

[0107] Table 3.

[0108] In the aforementioned embodiments, when TAHP reaches 4 wt% relative to TAEC+TBEC, the crosslinking time (tc90) increases significantly.

[0109] Example 4:

[0110] This experiment was conducted under the same conditions as in Example 1, except that Lup@TBHP (tert-butyl hydroperoxide) was used instead of TAHP. The results are shown in Table 4 below:

[0111]

[0112]

[0113] Table 4.

[0114] In the aforementioned embodiments, when TBHP reaches 4 wt% relative to pure TAEC, the crosslinking time (tc90) increases significantly.

[0115] Example 5:

[0116] This experiment was conducted under the same conditions as in Example 4, except that a mixture of 20% O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) and 80% O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC) was used instead of TAEC alone. The results are shown in Table 5 below:

[0117]

[0118] Table 5.

[0119] In the aforementioned embodiments, when TBHP reaches 4 wt% relative to TAEC+TBEC, the crosslinking time (tc90) increases significantly.

[0120] Example 6:

[0121] This experiment was conducted under the same conditions as in Example 4, except that a mixture of 50% O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) and 50% O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC) was used instead of TAEC alone. The results are shown in Table 6 below:

[0122]

[0123]

[0124] Table 6.

[0125] In the aforementioned embodiments, when TBHP reaches 4 wt% relative to TAEC+TBEC, the crosslinking time (tc90) increases significantly.

[0126] Example 7:

[0127] This experiment was conducted under the same conditions as in Example 1, except that OO-tert-amyl-O-2-isopropyl-monoperoxycarbonate (TAIC) was used instead of TAEC. The results are shown in Table 7 below:

[0128]

[0129] Table 7.

[0130] As can be seen from the table, by adding at least 0.4 wt% TAHP relative to TAEC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0131] Example 8:

[0132] This experiment was conducted under the same conditions as in Example 1, except that a mixture of 60% O,O-tert-amyl-O-2-isopropyl-monoperoxycarbonate (TAIC) and 40% O,O-tert-amyl-O-(2-ethylhexyl)monoperoxycarbonate (TAEC) was used instead of TAEC alone. The results are shown in Table 8 below:

[0133]

[0134] Table 8.

[0135] As can be seen from the table, by adding at least 0.4 wt% TAHP relative to TAIC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0136] Example 9:

[0137] This experiment was conducted under the same conditions as in Example 1, except that a polyolefin elastomer (KJ640T 27255C manufactured by JAPANPOLYETHYLENE CORPORATION) was used instead of EVA. The results are shown in Table 9 below:

[0138]

[0139] Table 9.

[0140] As can be seen from the table, by adding at least 0.4 wt% TAHP relative to TAEC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0141] Example 10:

[0142] This experiment was conducted under the same conditions as in Example 9, except that O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (TBEC) was used instead of O,O-tert-pentyl-O-(2-ethylhexyl) monoperoxycarbonate (TAEC). The results are shown in Table 10 below:

[0143]

[0144] Table 10.

[0145] As can be seen from the table, by adding at least 0.4 wt% TBHP relative to TBEC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0146] Example 11:

[0147] This experiment was conducted under the same conditions as in Example 9, except that O,O-tert-pentyl-O-2-isopropyl-monoperoxycarbonate (TAIC) was used instead of O,O-tert-pentyl-O-(2-ethylhexyl)monoperoxycarbonate (TAEC). The results are shown in Table 11 below:

[0148]

[0149] Table 11.

[0150] As can be seen from the table, by adding at least 0.4 wt% TAHP relative to TAIC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

[0151] Example 12:

[0152] This experiment was conducted under the same conditions as in Example 9, except that O,O-tert-butyl-O-2-isopropyl-monoperoxycarbonate (TBIC) was used instead of O,O-tert-pentyl-O-(2-ethylhexyl)monoperoxycarbonate (TAEC). The results are shown in Table 12 below:

[0153]

[0154] Table 12.

[0155] As can be seen from the table, by adding at least 0.4 wt% TBHP relative to TBIC, scorching was effectively prevented, while maintaining a high crosslinking rate (tc90) and a good crosslinking density (MH-ML).

Claims

1. Use of (b) at least one monoperoxycarbonate and (c) at least one tertiary alkyl hydroperoxide to improve crosslink density of an ethylene polymer, wherein the at least one monoperoxycarbonate is less than 2 parts by weight for 100 parts by weight of the ethylene polymer, wherein the at least one tertiary alkyl hydroperoxide is 0.4 to less than 4 parts by weight for 100 parts by weight of component (b), wherein the total amount of (b) and (c) is less than 2 parts by weight for 100 parts by weight of the ethylene polymer.

2. The use according to claim 1, wherein the ethylene polymer is an ethylene / vinyl acetate copolymer.

3. The use according to claim 1, wherein the ethylene polymer is a polyolefin elastomer.

4. The use according to any one of claims 1 to 3, wherein the monoperoxycarbonate is an OO-tertiary alkyl-O-alkyl monoperoxycarbonate.

5. The use according to claim 4, wherein the OO-tertiary alkyl-O-alkyl monoperoxycarbonate is selected from the group consisting of OO-tert-butyl-O-2-ethylhexyl-monoperoxycarbonate, OO-tert-butyl-O-2-isopropyl-monoperoxycarbonate, OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate, OO-tert-amyl-O-2-isopropyl-monoperoxycarbonate, and mixtures thereof.

6. The use according to claim 5, wherein the OO-tertiary alkyl-O-alkyl monoperoxycarbonate is selected from the group consisting of OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate, OO-tert-butyl-O-2-ethylhexyl-monoperoxycarbonate, mixtures thereof, and mixtures of OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate and OO-tert-amyl-O-2-isopropyl-monoperoxycarbonate.

7. The use according to claim 6, wherein the OO-tertiary alkyl-O-alkyl monoperoxycarbonate is selected from the group consisting of OO-tert-amyl-O-2-ethylhexyl-monoperoxycarbonate, OO-tert-butyl-O-2-ethylhexyl-monoperoxycarbonate, and mixtures thereof.

8. The use according to any one of claims 1 to 3, wherein the monoperoxycarbonate is 0.1 to less than 2 parts by weight for 100 parts by weight of the ethylene polymer.

9. The use according to claim 8, wherein the monoperoxycarbonate is 0.2 to 1.5 parts by weight for 100 parts by weight of the ethylene polymer.

10. The use according to any one of claims 1 to 3, wherein the tertiary alkyl hydroperoxide is selected from the group consisting of t-butyl hydroperoxide, t-amyl hydroperoxide, t-hexyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumyl hydroperoxide, 2,5-dimethyl-2,5-di-hydroperoxide (2,5-2,5), and mixtures thereof.

11. The use according to claim 10, wherein the tertiary alkyl hydroperoxide is t-amyl hydroperoxide.

12. The use according to any one of claims 1 to 3, wherein the tertiary alkyl hydroperoxide is 0.5 to 3.5 parts by weight for 100 parts by weight of component (b).

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