Composition comprising at least one monoperoxycarbonate and at least one t-alkyl hydroperoxide

Abstract

The present invention relates to a composition comprising at least one organic peroxide, corresponding to formula (I) as defined hereinafter, and at least one t-alkyl hydroperoxide, and to the use thereof for crosslinking crosslinkable polymers. The invention also relates to a crosslinkable composition comprising at least one polyolefin and at least one organic peroxide corresponding to formula (I) and at least one t-alkyl hydroperoxide. The present invention likewise relates to a method for preparing a crosslinkable-polymer-based material comprising at least one step of crosslinking a crosslinkable composition as defined previously.

Description

[0001] DESCRIPTION

[0002] TITLE: Composition comprising at least one monoperoxycarbonate and at least one t-alkyl hydroperoxide

[0003] The present invention relates to a composition comprising at least one organic peroxide, corresponding to formula (I) as defined below, and at least one t-alkyl hydroperoxide.

[0004] The invention also relates to the use of said composition for the crosslinking of crosslinkable polymers, preferably polyolefins, more preferably elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers, particularly intended for use in photovoltaic applications.

[0005] The invention also relates to a crosslinkable composition comprising at least one crosslinkable polymer, at least one organic peroxide as defined below, and at least one t-alkyl hydroperoxide.

[0006] The present invention also relates to a method for preparing a crosslinkable polymer-based material, preferably an encapsulating material, in particular for photovoltaic cells, comprising at least one crosslinking step of a crosslinkable composition as defined above.

[0007] The invention also relates to a crosslinkable polymer-based material that can be obtained by the process described above and a photovoltaic module comprising at least one such material.

[0008] Materials, preferably in film form, used for encapsulating photovoltaic cells are commonly designed from polyolefins, such as ethylene vinyl acetate (EVA) copolymers or elastomeric polyolefins (POE).

[0009] In order to acquire satisfactory thermomechanical properties for this application, particularly in terms of good adhesion properties to the module substrate, creep resistance and resistance to weathering degradation, it is important to crosslink the polyolefins and obtain a good crosslinking density.

[0010] Indeed, if the crosslinking density is too low, the resulting material is likely to exhibit, among other things, insufficient tensile and tear strength. Crosslinking agents typically used are organic peroxides such as dialkyl peroxides, peroxyesters, peroxyketals, peroxycarbonates, and mixtures thereof. As an example of a monoperoxycarbonate, OO-tert-butyl-O-(2-ethylhexyl monoperoxycarbonate (TBEC) is already known to be used for crosslinking polyolefins, particularly ethylene vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE).

[0011] During the photovoltaic module manufacturing process, the solar cells and their electrical conductors are sandwiched between two layers (or films) made from a polyolefin-based composition and one or more crosslinking agents. This manufacturing process involves a single step of laminating the various layers that make up the photovoltaic module at a specific temperature for a set period, during which the polyolefin-based composition crosslinks. The different layers of the module are thus compressed together, and the solar cells become embedded in a crosslinked polyolefin-based material.

[0012] However, the cross-linking of polyolefins with certain organic peroxides can cause yellowing, or even browning in some cases, of the material encapsulating photovoltaic cells. This phenomenon can thus induce a change in the transmittance of the incident light flux in the solar cells, which in turn reduces their power output over time.

[0013] Furthermore, the crosslinking of ethylene-vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE) often results in materials with mechanical properties, particularly tensile strength and tear resistance, that can decrease over time. Indeed, the crosslinking density can degrade over time due to environmental factors.

[0014] Furthermore, under the influence of ambient temperature and / or humidity, the organic peroxide added to polyolefins, particularly elastomeric polyolefins (POEs), to formulate the encapsulation film, can evaporate, leading to an insufficient degree of crosslinking of the material intended to encapsulate the photovoltaic cells. Finally, some crosslinking agents also have the disadvantage of being synthesized solely from fossil-based raw materials.

[0015] In view of the above, there is therefore a real need to propose a composition based on at least one bio-based crosslinking agent, exhibiting good crosslinking properties for crosslinkable polymers, in particular by giving them a satisfactory crosslinking density, while minimizing the risks of yellowing that may occur during the crosslinking of crosslinkable polymers.

[0016] In other words, one of the objectives of the present invention is to provide a bio-based agent that is at least as effective for crosslinking crosslinkable polymers intended for use in encapsulating photovoltaic cells as the crosslinking agents conventionally used today. The present invention therefore relates in particular to a composition (Cl) comprising: at least one monoperoxycarbonate corresponding to the following formula (I):

[0017] [Chem 1]

[0018] Formula (I) in which:

[0019] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, and

[0020] R2 represents a branched alkyl radical; and at least one t-alkyl hydroperoxide.

[0021] Preferably, the present invention relates to a composition (Cl) comprising: at least one monoperoxycarbonate corresponding to the following formula (I):

[0022] [Chem 1] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, and

[0023] R2 represents a branched alkyl radical; at least one t-alkyl hydroperoxide; and 0% to 3% by weight of a dialkyl peroxide, preferably 0 to 2% by weight, again preferably 0 to 1% by weight, again preferably 0 to 0.5% by weight relative to the total weight of organic peroxides.

[0024] The composition (Cl) according to the invention makes it possible to effectively crosslink crosslinkable polymers, preferably polyolefins, in particular polyolefins intended to be used for the encapsulation of photovoltaic cells, ensuring them a good crosslinking density, in particular stable over time.

[0025] The monoperoxycarbonate(s) in the composition according to the invention (Cl) has the advantage of having a bio-based origin, exhibiting good crosslinking properties for crosslinkable polymers, in particular polyolefins, and reducing the risks of yellowing that may occur during their crosslinking.

[0026] The monoperoxycarbonate(s) present in the composition according to the invention (Cl) has in particular a carbon content by weight predominantly of biological origin in relation to the total mass of carbon of the monoperoxycarbonate.

[0027] The monoperoxycarbonate(s) present in the composition according to the invention (Cl) preferably has a carbon content of biological origin greater than at least 30% by weight, preferably at least 50% by weight, more preferably at least 55% by weight, better at least 60% by weight, relative to the total mass of carbon of the monoperoxycarbonate.

[0028] The composition according to the invention (Cl) makes it possible to obtain polymer-based materials, preferably polyolefin-based, crosslinked materials having good mechanical properties.

[0029] Thus the use of the composition according to the invention (Cl) is at least as effective for the crosslinking of polymers, in particular polyolefins, as compositions based on crosslinking agents conventionally used in the prior art, while being more environmentally friendly and / or safer for the health of users.

[0030] In particular, the composition according to the invention (Cl) allows for less evaporation of organic peroxides than other crosslinking agents conventionally used in the prior art.

[0031] Another aspect of the present invention relates to the use of at least the composition (Cl), as defined above, for the crosslinking of at least one crosslinkable polymer, preferably at least one polyolefin.

[0032] The invention also relates to a crosslinkable composition (CR) comprising at least one crosslinkable polymer, preferably at least one polyolefin, more preferably chosen from the group consisting of ethylene vinyl acetate (EVA) copolymers, elastomeric polyolefins (POE) and mixtures thereof, at least one monoperoxycarbonate corresponding to formula (I), as defined above, and at least one t-alkyl hydroperoxide.

[0033] The crosslinkable composition (CR) according to the invention makes it possible to produce a material, in particular an encapsulation or sealing material, preferably for photovoltaic cells, having thermomechanical properties suitable for the applications sought, with high production.

[0034] The crosslinkable composition (CR) according to the invention thus has the advantage of crosslinking during a manufacturing process of a photovoltaic module.

[0035] Furthermore, the present invention relates to a crosslinking process of a composition comprising at least one crosslinkable polymer, comprising at least one crosslinking step of said polymer with at least one composition (Cl) comprising at least one monoperoxycarbonate corresponding to formula (I) as defined above and at least one t-alkyl hydroperoxide.

[0036] The process according to the invention makes it possible to obtain a high reaction rate, and therefore rapid crosslinking of the polymers, while maintaining good crosslinking density. Thus, materials based on crosslinked polymers with at least one composition (Cl) according to the invention exhibit good mechanical properties.

[0037] Furthermore, the present invention also relates to a method for manufacturing a material comprising at least one crosslinking step of a crosslinkable composition as defined above. The method according to the invention thus has the advantage of producing a material with good thermomechanical properties and in which any structural imperfections are minimized.

[0038] Similarly, another object of the invention relates to the material comprising at least one crosslinked polymer, preferably crosslinked polyolefin, with at least one composition (Cl) according to the invention.

[0039] The material obtained is preferably a solar cell encapsulation material.

[0040] The invention also relates to a photovoltaic module comprising such a material encapsulating solar cells.

[0041] The photovoltaic module exhibits improved properties thanks to the presence of the encapsulating material.

[0042] Other features and advantages of the invention will become clearer upon reading the description and examples that follow.

[0043] In what follows, and unless otherwise indicated, the bounds of a domain of values ​​are included within that domain.

[0044] The expression "at least one" is equivalent to the expression "one or more".

[0045] Composition (Cl)

[0046] The monoperoxycarbonate(s) present in the composition according to the present invention (Cl) correspond(s) to the following formula (I):

[0047] [Chem 1]

[0048] Formula (I) in which:

[0049] Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, preferably less than or equal to 10, and

[0050] R2 represents a branched alkyl radical.

[0051] Preferably, in formula (I), R2 represents a branched alkyl radical at C4-C10, more preferably at C4-C8. Preferably, in formula (I), R2 represents a branched alkyl radical at C4, C5 or Cs, more preferably at C4.

[0052] Preferably, in formula (I), Ri represents a linear alkyl radical in C1-C12, more preferably in C2-C12, even more preferably in C4-C12, better in C6-C12.

[0053] Preferably, in formula (I), Ri represents a linear alkyl radical in C1-C10, more preferably in C2-C10, even more preferably in C4-C10, better in C0-C10.

[0054] According to a preferred embodiment, in formula (I):

[0055] • Ri represents a linear alkyl radical in C1-C12, more preferentially in C2-C12, even more preferentially in C4-C12, and even better in C6-C12.

[0056] • R2 represents a branched alkyl radical in C4-C10, more preferentially in C4-C8.

[0057] According to a preferred embodiment, in formula (I):

[0058] • Ri represents a linear alkyl radical in C1-C10, more preferentially in C2-C10, even more preferentially in C4-C10, and even better in C0-C10.

[0059] • R2 represents a branched alkyl radical in C4-C10, more preferentially in C4-C8.

[0060] Preferably, the monoperoxycarbonate(s) of formula (I) correspond(s) to the following formula (F):

[0061] [Chem 2]

[0062] Formula (F) in which:

[0063] R2 represents a branched alkyl radical as defined previously in formula (I).

[0064] Preferably, in formula (F), R2 represents a branched alkyl radical in C4-C10, more preferably in C4-C8, better in C4, C5 or Cs, even better in Cs. Preferably, the monoperoxycarbonate(s) is / are chosen from the group consisting of:

[0065] [Chem 3] OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC),

[0066] [Chem 4] OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC),

[0067] [Chem 5] OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), and their mixtures.

[0068] More preferably, the monoperoxycarbonate is OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC).

[0069] As previously stated, the composition according to the invention (Cl) further comprises at least one t-alkyl hydroperoxide.

[0070] Preferably, t-alkyl hydroperoxide is chosen from the group consisting of t-butyl hydroperoxide (TBHP), t-amyl hydroperoxide (TAHP), t-hexyl hydroperoxide (THHP), 1,1,3,3-tetramethylbutyl hydroperoxide (TOHP), paramenthane hydroperoxide (PMHP), 2,5-dimethyl-2,5-dihydroperoxide (2,5-2,5) and mixtures thereof.

[0071] Preferably, t-alkyl hydroperoxide is t-butyl hydroperoxide (TBHP).

[0072] Preferably, in the composition according to the invention (Cl), the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (!') is less than 0.5, preferably less than 0.1, more preferably less than 0.05, more preferably less than 0.04.

[0073] Preferably, in the composition according to the invention (Cl), the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (F) is greater than 0.0001, preferably greater than 0.0005, more preferably greater than 0.001, more preferably greater than 0.003.

[0074] Preferably, in the composition according to the invention (Cl), the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (!') is in the range of 0.0001 to 0.5, preferably from 0.0005 to 0.1, more preferably from 0.001 to 0.05, more preferably from 0.003 to 0.04.

[0075] The composition according to the invention (Cl) may comprise a dialkyl peroxide, in a content of less than 3%, preferably less than 2%, more preferably less than 1%, more preferably less than 0.5% by weight relative to the total weight of organic peroxides.

[0076] In other words, the composition according to the invention (Cl) can comprise from 0% to 3% by weight of a dialkyl peroxide, preferably from 0 to 2% by weight, more preferably from 0 to 1% by weight, more preferably from 0 to 0.5% by weight relative to the total weight of organic peroxides.

[0077] Preferably, the weight ratio between the dialkyl peroxide and at least one monoperoxycarbonate corresponding to formula (I) is less than 0.04, preferably less than 0.03, more preferably less than 0.01, more preferably less than 0.005. When several dialkyl peroxides are present, or when several monoperoxycarbonates are present, the weight ratio between the dialkyl peroxide(s) and the monoperoxycarbonate(s) corresponding to formula (I) is less than 0.04, preferably less than 0.03, more preferably less than 0.01, more preferably less than 0.005.

[0078] Preferably, the composition according to the invention (Cl) does not comprise dialkyl peroxide. Method for preparing the composition (Cl)

[0079] The present invention also relates to a method for preparing the composition (Cl) as defined above, comprising at least one step of mixing at least one monoperoxycarbonate, as described above, and at least one t-alkyl hydroperoxide as defined above.

[0080] Advantageously, the mixing step can be implemented in conventional devices such as continuous mixers and mixer-extruders, preferably at a temperature below the degradation temperature of the monoperoxycarbonates of the invention.

[0081] Use of the composition (Cl)

[0082] As previously stated, an object of the present invention relates to the use of at least one composition (Cl), as defined above, for the crosslinking of at least one crosslinkable polymer, preferably at least one polyolefin.

[0083] For the purposes of this invention, "polyolefin" means a polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc.

[0084] For the purposes of this invention, "derived from" means that the motifs of the main chain of the polymer and / or the adjacent chains (or dangling chains) of the polymer result from the polymerization or copolymerization of the monomers from which the polymer is made.

[0085] Preferably, the polyolefin is chosen from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures.

[0086] Preferably, the polyolefin is chosen from the group consisting of elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers.

[0087] For the purposes of this invention, "polyolefin elastomer" (POE) means an elastomeric polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc. Preferably, the polyolefin elastomer is a copolymer of ethylene and an alpha-olefin selected from butene and octene.

[0088] For the purposes of this invention, "elastomer" means a polymer capable of undergoing uniaxial deformation at room temperature, preferably of at least 20% for a period of fifteen minutes, and of returning to its original shape, preferably with a residual deformation of less than 5% compared to its original shape, when this stress is no longer exerted.

[0089] The thermoplastic and / or elastomeric polymers used according to the invention can be defined as natural or synthetic polymers that have thermoplastic and / or elastomeric properties and that can be crosslinked (cured) by the action of a crosslinking agent. The crosslinking action and crosslinkable polymers are described in Rubber World, "Elastomer Crosslinking with Diperoxyketals," October 1983, pages 26-32, and in Rubber and Plastic News, "Organic Peroxides for Rubber Crosslinking," September 29, 1980, pages 46-50. Polyolefins suitable for the present invention are described in Modern Plastics Encyclopedia 89, pages 63-67, 74-75.

[0090] Examples of polymers and / or elastomers include linear low-density polyethylene, low-density polyethylene (LDPE), high-density polyethylene (HDPE), chlorinated polyethylene, ethylene-propylene-diene terpolymers (EPDM), ethylene-vinyl acetate (EVA) copolymers, polyolefin elastomers, for example ethylene-propylene copolymers, ethylene-butene copolymers, silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene (NBR) copolymers, styrene-butadiene (SBR) copolymers, chlorosulfonated polyethylene or fluoroelastomers, ethylene-(meth)methyl acrylate copolymers, ethylene-glycidyl methacrylate copolymers and mixtures thereof.

[0091] According to one embodiment, the crosslinkable polymers are devoid of chlorine functional groups and carboxylic acid functional groups, preferably devoid of halogen functional groups and carboxylic acid functional groups.

[0092] Polyethylene can include homopolymers and copolymers such as linear low-density polyethylene, low-density polyethylene (LDPE), high-density polyethylene (HDPE), chlorinated polyethylene, and ethylene-propylene-diene terpolymers (EPDM).

[0093] Preferably, crosslinkable polymers are chosen from the group consisting of polyethylene, ethylene-vinyl acetate (EVA) copolymers, ethylene-butene copolymers, polyethylene, rubber, ethylene-propylene-diene (EPDM) terpolymers and their mixtures, more preferably chosen from the group consisting of ethylene-vinyl acetate (EVA) copolymers.

[0094] Ethylene and vinyl acetate (EVA) copolymers suitable for the present invention are, for example, the ethylene-vinyl acetate copolymers sold respectively under the trade names "Evatane® 24-03, 24-03 SA, 28-03, 28-05, 28-25, 28-40, 28-150, 28-420, 28-800, 33-15, 33-25, 33-45 PV, 33-400, 34-50 PV" by SK Chemicals.

[0095] The vinyl acetate content of the ethylene-vinyl acetate copolymers suitable for the present invention can vary: for example, these copolymers can be low vinyl acetate or high vinyl acetate.

[0096] Preferably, the invention relates to the use of at least one composition according to the invention (Cl) for the crosslinking of at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and their mixtures, in particular elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers.

[0097] Preferably, the invention relates to the use of at least one composition (Cl) comprising OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC) and t-alkyl hydroperoxide for the crosslinking of at least one crosslinkable polymer, preferably at least one polyolefin.

[0098] Monoperoxycarbonate synthesis process

[0099] The monoperoxycarbonate of formula (I) according to the invention can be prepared by reacting at least one alkyl chloroformate of formula Ri-O-(C=O)C1, with Ri as defined above, and at least one organic hydroperoxide of formula R2-O-OH with R2 as defined above. In other words, the process for synthesizing a monoperoxycarbonate of formula (II) comprises at least one reaction step (a2) of alkyl chloroformate, as defined above, and at least one organic hydroperoxide of formula R2-O-OH with R2, as defined above.

[0100] The reaction step (a2) can take place at a temperature ranging from -10 to 30°C.

[0101] The reaction step (a2) can take place in the presence of a nonpolar solvent.

[0102] Alkyl chloroformate can be prepared by reacting at least one alcohol Ri-OH, with Ri as defined above, with COCI2, preferably at a temperature ranging from 5 to 30°C, in the presence or absence of a solvent, such as benzene.

[0103] Alkyl chloroformate can alternatively be prepared by reacting at least one alcohol of formula Ri-OH, with Ri as defined above, with phosgene, preferably at a temperature ranging from -15°C to 0°C.

[0104] Crosslinkable composition (CR)

[0105] As previously stated, the crosslinkable composition (CR) comprises: at least one crosslinkable polymer, preferably at least one polyolefin, as defined above and at least one monoperoxycarbonate corresponding to formula (I), as defined above, and at least one t-alkyl hydroperoxide as defined above.

[0106] The monoperoxycarbonate(s) corresponding to formula (I) or (I') may be present in the crosslinkable composition (CR) at a content of 0.1 to 5 by weight, preferably 0.2 to 1.5, more preferably 0.3 to 1, more preferably 0.4 to 1, more preferably 0.4 to 0.7 by weight, relative to 100 parts by weight of the crosslinkable polymer as defined above.

[0107] Advantageously, the crosslinkable composition (CR) comprises: at least one monoperoxycarbonate selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), at least one polyolefin selected from the group consisting of elastomeric polyolefins (POE) and ethylene-vinyl acetate (EVA) copolymers and mixtures thereof, in particular elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers, and at least one t-alkyl hydroperoxide, preferably TBHP.

[0108] The crosslinkable composition (CR) may further comprise at least one additional organic peroxide other than the monoperoxycarbonate(s) of formula (I) as described above.

[0109] Preferably, the crosslinkable composition (CR) further comprises at least one additional monoperoxycarbonate different from the monoperoxycarbonate(s) of formula (I) as described above.

[0110] Preferably, the additional monoperoxycarbonate is also different from OO-tert-butyl-O-(2-ethylhexyl)monoperoxycarbonate (TBEC).

[0111] The monoperoxycarbonate(s), other than the monoperoxycarbonate of formula (I), preferably corresponds to the following formula (III):

[0112] [Chem 6]

[0113] Formula (III) in which:

[0114] R'i represents a branched alkyl radical comprising a number of carbon atoms less than or equal to 6 and

[0115] R'2 represents an alkyl radical.

[0116] Preferably, in formula (III), R'i represents a branched alkyl radical comprising a number of carbon atoms less than or equal to 6 and R'2 represents a branched alkyl radical.

[0117] Preferably, in formula (III), R'i and R'2 are different.

[0118] According to formula (III), R'i is preferably a C2-C5 branched alkyl radical. Preferably, R'i is a C3 branched alkyl radical.

[0119] (isopropyl). According to formula (III), R'2 is preferably a C1-C10 alkyl radical, preferably C4-C8. Preferably, R'2 is a C4 or C5 alkyl radical, in particular branched at C5 (tert-amyl) or Ce (tert-hexyl).

[0120] Advantageously, R'i is a C2-C5 branched alkyl radical, and R'2 is a C1-C10 alkyl radical, specifically a C4-C8 alkyl radical.

[0121] Preferably, the monoperoxycarbonate of formula (III) is chosen from the group consisting of tert-amyl peroxy isopropyl monocarbonate (TAIC), tert-butyl peroxy isopropyl monocarbonate (TBIC), tert-octyl peroxy isopropyl monocarbonate (TOIC) and tert-hexyl peroxy isopropyl monocarbonate (THIC).

[0122] More preferably, the monoperoxycarbonate corresponding to formula (III) is tert-amyl peroxy isopropyl monocarbonate (TAIC).

[0123] Monoperoxycarbonate, different from monoperoxycarbonate of formula (I), may be present in the crosslinkable composition (CR) at a content of 0.1 to less than 5 parts by weight, preferably 0.2 to 1.5, more preferably 0.3 to 1, more preferably 0.4 to 1, more preferably 0.4 to 0.7 and even more preferably about 0.5 parts by weight, per 100 parts by weight of the crosslinkable polymer as defined above.

[0124] According to a preferred embodiment, the total amount of organic peroxide in the crosslinkable composition (CR) is less than 3 parts by weight per 100 parts by weight of the crosslinkable polymer, more preferably less than 1.5 parts by weight per 100 parts by weight of the crosslinkable polymer.

[0125] According to a preferred embodiment, the crosslinkable composition (CR) comprises at least one crosslinkable polymer, preferably at least one polyolefin, as defined above, at least one monoperoxycarbonate of formula (I) or (I'), at least one t-alkyl hydroperoxide, and at least one monoperoxycarbonate of formula (III).

[0126] Preferably, the crosslinkable composition (CR) comprises at least one polyolefin, as defined above, OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), t-amyl hydroperoxide (TBHP), and tert-amyl peroxyisopropyl monocarbonate (TAIC).

[0127] The crosslinkable composition (CR) may also include at least one co-agent, which is not an organic peroxide. Advantageously, said co-agent comprises at least one carbamate, maleimide, acrylate, methacrylate, or allyl functional group. Allyl carboxylates may be used, which may be selected from the group consisting of allyl, diallyl, and triallyl types.

[0128] Said co-agent may be selected from the group consisting of divinylbenzene, diisopropenylbenzene, alpha-methylstyrene, alpha-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, diurethane dimethacrylate, trimethylolpropane trimethacrylate, bisphenol A epoxy diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycol ethoxylate diacrylate,butanediol diacrylate, hexanediol diacrylate, aliphatic urethane diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, glycerol propoxylate triacrylate, aliphatic urethane triacrylate, trimethylolpropane triacrylate and dipentaerythritol pentaacrylate, triallyl cyanurate (TAC), triallyl isocyanurate, N,N'-m-phenylenedimaleimide, butadiene, chloroprene and isoprene.

[0129] More preferably, the co-agent is chosen from the group consisting of: triallyl cyanurate, triallyl isocyanurate, N,N'-m-phenylenedimide, triallyl trimellitate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, preferably is chosen from the group consisting of: triallyl cyanurate (TAC), triallyl isocyanurate, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane trimethacrylate (TMPTMA) and even more preferably is triallyl isocyanurate.

[0130] The said co-agent may be present from 0.05% to 30%, preferably from 0.1% to 10% by weight relative to the total weight of the composition.

[0131] The crosslinkable composition (CR) may further include one or more additives such as coupling agents, UV stabilizers, UV absorbers, fillers, plasticizers, flame retardants, antioxidants, colorants, organic or mineral pigments, and mixtures thereof. Examples of coupling agents include monoalkyl titanates, (vinyl)trichlorosilanes, and (vinyl)trikoxysilanes, particularly 3-methacryloxypropyltrimethoxysiloxane. They may represent from 0.01 to 5% by weight relative to the weight of the ethylene polymer.

[0132] UV stabilizers can be selected from masked amine optical stabilizers (HALS), while UV absorbers can be selected, for example, from benzophenones, triazines, and benzotriazoles. These compounds can represent from 0.01 to 3% by weight relative to the weight of ethylene polymer.

[0133] Inorganic fillers such as silicon dioxide, alumina, talc, and calcium carbonate can be added to increase mechanical strength, although nanometric clays are preferred because of the transparency they provide.

[0134] Organic or mineral pigments can also be added to color the crosslinkable composition. Titanium dioxide, in particular, can be used to obtain a white color, which is especially useful when the composition is used to manufacture a film for the backing of photovoltaic panels.

[0135] Examples of plasticizers include paraffinic or aromatic mineral oils, phthalates, azelates, adipates and the like.

[0136] Antioxidants can be phenolic, phosphate, or sulfur-containing. Alternatively, quinolines, such as 1,2-dihydro-2,2,4-trimethylquinoline, can be used as antioxidants.

[0137] According to a preferred embodiment, the crosslinkable composition (CR) of this invention does not comprise any aromatic peroxide such as dicumyl peroxide.

[0138] Process for preparing the crosslinkable composition (CR)

[0139] The present invention also relates to a method for preparing the crosslinkable composition (CR) as defined above, comprising at least one step of mixing at least one crosslinkable polymer, preferably at least one polyolefin, as described above, and at least one composition (Cl) as defined above.

[0140] In other words, the process for preparing the crosslinkable composition (CR), as defined above, includes at least one step of mixing at least one crosslinkable polymer, preferably at least one polyolefin, as described above, with at least one monoperoxycarbonate of formula (I) as described above, and at least one t-alkyl hydroperoxide, and optionally with at least one monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), preferably corresponding to formula (III) as described above.

[0141] Advantageously, the mixing step can be implemented in conventional devices such as continuous mixers and mixer-extruders, preferably at a temperature below the degradation temperature of the monoperoxycarbonates of the invention.

[0142] crosslinking process

[0143] Another aspect of the present invention lies in a crosslinking process of at least one crosslinkable polymer, preferably at least one polyolefin, as defined above, comprising at least one crosslinking step of said crosslinkable polymer, with at least one composition (Cl) according to the invention.

[0144] The crosslinking step is preferably carried out at a temperature ranging from 130 to 180°C, more preferably ranging from 140 to 165°C.

[0145] Preferably, the said crosslinking step is carried out for a period of 8 to 30 minutes, more preferably from 12 to 25 minutes.

[0146] Crosslinked polymer

[0147] Furthermore, the present invention also relates to a polymer, preferably a polyolefin, as defined above, crosslinked with at least one composition (Cl) according to the invention as defined above.

[0148] In other words, the invention relates to a crosslinked polymer, preferably a crosslinked polyolefin, obtainable by a crosslinking process employing at least one composition (Cl) according to the invention as defined above. Said polyolefin is as defined above, in particular is chosen from the group consisting of ethylene-vinyl acetate (EVA) copolymers and elastomeric polyolefins (POE) and mixtures thereof, preferably ethylene-vinyl acetate (EVA) copolymers or elastomeric polyolefins (POE).

[0149] Preferably, the crosslinking process is as defined previously.

[0150] Process for manufacturing a material from the crosslinkable composition (CR)

[0151] The invention also relates to a method for manufacturing a material comprising (a) at least one crosslinking (or hardening) step of a crosslinkable composition (CR) as defined above.

[0152] The material is notably chosen from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible hoses (including pipes for automotive radiators, drinking water and underfloor heating, for example), roller coatings, rotary moldings, honeycomb articles, and shoe soles.

[0153] Advantageously, the material is a solar cell encapsulation material.

[0154] Preferably, the crosslinking (or hardening) step consists of a rolling step.

[0155] Preferably, the crosslinking step (a) is carried out at a temperature ranging from 130 to 180°C, more preferably ranging from 140 to 165°C.

[0156] Preferably, said crosslinking step (a) is carried out for a period of 8 to 30 minutes, more preferably from 12 to 25 minutes.

[0157] Preferably, the process includes a step preceding and / or concurrent (a') with the crosslinking step (a) selected from the group consisting of molding, extrusion, and injection of the composition as defined above. When the material is a solar cell encapsulation material, this step is preferably an extrusion step.

[0158] Step (a') can be carried out to obtain a sheet with a thickness of 50 to 2000 µm, preferably 100 to 1000 µm, for example. This step (a') can be carried out with a T-die extruder or, alternatively, a twin-screw extruder coupled to a twin-roll mill.

[0159] Preferably, step (a') is conducted at a temperature ranging from 80 to 150 °C, more preferably ranging from 90 to 120 °C.

[0160] Preferably, no crosslinking is obtained during step (a').

[0161] In a particular embodiment, steps (a') and (a) are carried out in a single step.

[0162] Manufacturing process for a photovoltaic module

[0163] According to one embodiment, the present invention relates to a method for manufacturing a photovoltaic module comprising:

[0164] (i) at least one rolling step of an assembly comprising successively:

[0165] • a first transparent layer forming the front face of a photovoltaic module,

[0166] • a layer obtained from the crosslinkable composition according to the invention,

[0167] • a plurality of solar cells arranged side by side and electrically connected to each other,

[0168] • a layer obtained from the crosslinkable composition according to the invention,

[0169] • a second layer or a multilayer assembly forming the back face (or support) of the module

[0170] (ii) optionally, at least one step of pressing the laminated layers together during step (i).

[0171] The pressing step can be carried out using conventional techniques, under heating and / or vacuum, for example at a temperature of 130 to 180 °C, more preferably 140 to 165 °C under vacuum, for a curing time that can vary from 8 to 30 minutes, for example from 8 to 25 minutes. The composition of the invention can be crosslinked during this pressing step or subsequently.

[0172] Preferably, the process comprises a single simultaneous pressing and curing (or crosslinking) step. Polyolefin-based material

[0173] Similarly, another object of the invention relates to a material comprising at least one crosslinked polymer, preferably a crosslinked polyolefin, with at least one monoperoxycarbonate corresponding to formula (I) as defined above, preferably at least one monoperoxycarbonate of formula (I'), (II) or (II'), in particular selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), and mixtures thereof.

[0174] In other words, an object of the invention is a material comprising at least one crosslinked polymer, preferably a crosslinked polyolefin, capable of being obtained by a crosslinking process using at least one monoperoxycarbonate of formula (I) as defined above, preferably at least one monoperoxycarbonate of formula (I'), (II) or (II'), in particular selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), and mixtures thereof.

[0175] The material obtained is preferably chosen from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible hoses (including pipes for automotive radiators, drinking water and underfloor heating, for example), roller coatings, rotary moldings, honeycomb articles and shoe soles.

[0176] Advantageously, the material is an encapsulation material, and even more preferably a solar cell encapsulation material.

[0177] Even more advantageously, the encapsulation material is a transparent film placed between the solar cells and the glass panel forming the front face of a photovoltaic module (upper glass panel), or a transparent or tinted film placed between the glass panel forming the rear face of the module (lower glass panel) and the solar cells in the case of bi-glass processes.

[0178] Thus, the material is preferentially used in a photovoltaic module manufacturing process, particularly in a double-glass process. More preferably, the material comprising a polyolefin, as defined above, is a film, in particular an ethylene polymer film, especially a film of homogeneously linear and branched ethylene and alpha-olefin copolymers.

[0179] The material according to the invention exhibits improved crosslinking density and a marked reduction, or even the absence, of gridding problems. This allows for the production of films free of surface defects and with good resistivity.

[0180] Photovoltaic module

[0181] The invention also relates to a photovoltaic module comprising at least one solar cell encapsulation material as described above.

[0182] In particular, the photovoltaic module according to the invention comprises at least:

[0183] • a first transparent layer forming the front face of the photovoltaic module and designed to receive a luminous flux,

[0184] • an encapsulating material, as described above, for a plurality of solar cells arranged side by side and electrically connected to each other,

[0185] • a second layer or multilayer assembly forming the back face (or support) of the photovoltaic module; the material encapsulating the plurality of solar cells being located between the first layer and the second layer or multilayer assembly.

[0186] The following examples serve to illustrate the invention but are not intended to be limiting.

[0187] EXAMPLES

[0188] 1. Example of alkyl chloroformate synthesis

[0189] Synthesis of n-octyl chloroformate (according to the process described in document CN112441923)

[0190] 325 parts by weight of n-octanol are introduced into a reactor and then cooled to -15°C. Phosgene is then added while the temperature is gradually raised to around -5°C / -2°C. The mixture is then heated to around 20°C-25°C and allowed to react for up to 2 hours.

[0191] Next, nitrogen gas is introduced at a temperature of 15°C to remove excess phosgene and hydrochloric acid to obtain n-octyl chloroformate.

[0192] 2. Examples of monoperoxycarbonate synthesis

[0193] Synthesis of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC)

[0194] 45.3g of a 30% wt. potassium hydroxide solution in water is loaded into a reactor. Then 28.4g of a 70% wt. tert-butyl hydroperoxide (TBHP) commercial solution in water is gradually added.

[0195] Next, 35g of n-octyl chloroformate is introduced while maintaining the reactor at 0°C. After the introduction of the chloroformate, the reactor temperature is raised to 5° / 10°C and the reaction is allowed to continue for 120 min.

[0196] After stopping the stirring and allowing the sediment to settle, the organic phase is collected and washed with sodium hydroxide, then with water. After washing, 41.5 g of organic phase are recovered, containing 99% by weight of TBOC.

[0197] 3. Ingredients used

[0198] In the following examples, the following ingredients were used:

[0199] TBOC: OO-tert-butyl-O-octylmonoperoxycarbonate (prepared according to the previous section), Luperox® TBEC: OO-tert-butyl-(2-ethylhexyl) monoperoxycarbonate (sold by Arkema)

[0200] Luperox® TBHP: tert-butyl hydroperoxide (sold by Arkema)

[0201] TAIC: crosslinking co-agent (sold by Sigma Aldrich)

[0202] Evatane® 28-25: Ethylene-vinyl acetate (EVA) copolymer with 28% by weight of vinyl acetate and having a melt flow index (MFI) of 25 g / 10 minutes, measured at 190°C, according to ASTM 1238.

[0203] POE Engage® PV 8669: Ethylene / 1-octene copolymer (POE) having a melt flow index (MFI) of 14 g / 10 minutes, measured at 190°C, according to ASTM D 1238 (sold by Dow Chemicals).

[0204] KH570: 3-methacryloxy-propyltrimethoxysiloxane (sold by Sigma Aldrich)

[0205] 4. Composition Formulations

[0206] 4.1. Tested compositions

[0207] Compositions (Al) and (A2) according to the invention and the comparative composition (Bl) were prepared from the ingredients indicated in Table 1 below.

[0208] In Table 1, the quantities of ingredients are indicated in parts per hundred parts of the polyolefm used (phr).

[0209] [Table 1] 4.2. Protocol

[0210] Polyolefin (POE) is introduced into a mixer (Rheomix 600 from Thermo Scientific equipped with two Banbury-type rotors) running (50 revolutions / minute, temperature at 40°C) and plasticized for approximately 4 minutes.

[0211] For composition A2, a premixing of monoperoxycarbonate and tert-butyl hydroperoxide is carried out.

[0212] The organic peroxy(s) and additives are then added, and mixing continues for 6 minutes. The final internal temperature of the mixer is between 50°C and 65°C.

[0213] Each recovered mixture is then passed through a calender (Comerico Ercole equipped with two cylinders) to obtain a film with a thickness of approximately 2 millimeters.

[0214] This results in four films with a thickness of approximately 2 millimeters.

[0215] Comparative measurements using the RPA Rheometer at a temperature of 145°C, under the conditions indicated in Table 2, were performed on each film following ASTM D5289 A.

[0216] [Table 2]

[0217] For the three films resulting from compositions (Al), (A2), and (Bl), the following parameters are measured:

[0218] MH-ML (units in dN.m) corresponds to the crosslinking density, T90 (units in minutes) corresponds to the crosslinking time to reach 90% of the MH-ML value

[0219] TS1 (units in minutes) corresponding to the toasting time (premature crosslinking). Measurements of these parameters were carried out 24 hours after the films were made.

[0220] 5. Results

[0221] Measurements were taken three times for each parameter evaluated. Table 3 shows the average obtained over the three measurements for each of the parameters tested.

[0222] [Table 3]

[0223] We observe that the crosslinking density (MH-ML) and the crosslinking speed (T90) are similar between the 3 samples; on the roasting time (Tsl), this is significantly longer for the samples containing TBOC (Al and A2), and in particular on sample A2.

[0224] 6. Yellowing Index (YI) Measurements

[0225] After measurements on RP A rheometer, the yellowing indices (YI) are measured using a spectrophotometer (X-Rite Model SP60) for each film.

[0226] The results are summarized in the following table 4:

[0227] [Table 4]

[0228] It is observed that TBOC leads to less yellowing than the

[0229] TBEC. General conclusion

[0230] It is observed that the composition according to the invention is as effective as Luperox ® TBEC in terms of crosslinking, allows for longer roasting time, while having a bio-based origin.

Claims

DEMANDS 1. Composition (Cl) comprising: at least one monoperoxycarbonate corresponding to the following formula (I): [Chem 1] Formula (I) in which: Ri represents a linear alkyl radical comprising a number of carbon atoms strictly less than 12, R2 represents a branched alkyl radical; at least one t-alkyl hydroperoxide; and 0% to 3% by weight of a dialkyl peroxide, preferably 0 to 2% by weight, again preferably 0 to 1% by weight, again preferably 0 to 0.5% by weight relative to the total weight of organic peroxides.

2. Composition (Cl) according to the preceding claim, characterized in that, in formula (I), R2 represents a C4-C10 branched alkyl radical, preferably a C4-C8 branched alkyl radical, more preferably a C4, C5 or Cs branched alkyl radical, better branched at C4.

3. Composition (Cl) according to claim 1 or 2, characterized in that, in formula (I), Ri represents a linear alkyl radical in C1-C10, preferably a linear alkyl radical in C2-C10, more preferably a linear alkyl radical in C4-C10, better a linear alkyl radical in C0-C10.

4. Composition (Cl) according to any one of the preceding claims, characterized in that the monoperoxycarbonate(s) of formula (I) correspond(s) to the following formula (I'): [Chem 2] Formula (!') in which: R2 represents a branched alkyl radical, preferably a C4-C10 branched alkyl radical, more preferably a C4-C8 branched alkyl radical.

5. Composition (Cl) according to any one of the preceding claims, characterized in that the monoperoxycarbonate(s) is or are selected from the group consisting of OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC), OO-tert-amyl-O-octylmonoperoxycarbonate (TAOC), OO-tert-octyl-O-octylmonoperoxycarbonate (TOOC), preferably OO-tert-butyl-O-octylmonoperoxycarbonate (TBOC).

6. Composition (Cl) according to any one of the preceding claims, characterized in that t-alkyl hydroperoxide is selected from the group consisting of: t-butyl hydroperoxide (TBHP), t-amyl hydroperoxide (TAHP), t-hexyl hydroperoxide (THHP), 1,1,3,3-tetramethylbutyl hydroperoxide (TOHP), paramenthane hydroperoxide (PMHP), 2,5-dimethyl-2,5-dihydroperoxide (2,5-2,5) and mixtures thereof, preferably said t-alkyl hydroperoxide being TBHP.

7. Composition according to any one of the preceding claims, wherein the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (T) is less than 0.5, preferably less than 0.1, more preferably less than 0.05, more preferably less than 0.

04.

8. Composition according to any one of the preceding claims, wherein the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (T) is greater than 0.0001, preferably greater than 0.0005, more preferably greater than 0.001, more preferably greater than 0.

003.

9. Composition according to any one of the preceding claims, wherein the weight ratio between the t-alkyl hydroperoxide(s) and the monoperoxycarbonate(s) of formula (I) or (T) is in the range of 0.0001 to 0.5, preferably 0.0005 to 0.1, more preferably 0.001 to 0.05, more preferably 0.003 to 0.

04.

10. Use of at least one composition (Cl) as defined according to any one of the preceding claims, for the crosslinking of at least one crosslinkable polymer, preferably at least one polyolefin.

11. Use according to the preceding claim, characterized in that the polyolefin is selected from the group consisting of elastomeric polyolefins (POE), ethylene-vinyl acetate (EVA) copolymers and mixtures thereof, more preferably selected from the group consisting of elastomeric polyolefins (POE) or ethylene-vinyl acetate (EVA) copolymers.

12. Crosslinkable composition (CR) comprising: at least one crosslinkable polymer, as defined according to claim 10 or 11, at least one monoperoxycarbonate corresponding to formula (I), as defined according to any one of claims 1 to 5, at least one t-alkyl hydroperoxide as defined according to claim 1 or 6.

13. A method for preparing a crosslinkable composition, as defined in the preceding claim, comprising at least one step of mixing at least one crosslinkable polymer, as defined in claim 10 or 11, and at least one composition (Cl) as defined in any one of claims 1 to 6.

14. A method for manufacturing a material comprising (a) at least one crosslinking step of a crosslinkable composition (CR) as defined in claim 9, the material is preferably selected from the group consisting of an encapsulation material, in particular a solar cell encapsulation material, wire and cable insulation, pipes and flexible tubing, roller coatings, rotary moldings, honeycomb articles, and shoe soles.

15. Material comprising at least one crosslinked polyolefin capable of being obtained by a crosslinking process employing at least one composition as defined in claim 11.

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