EP3724263A1

EP3724263A1 - Use of a mixture of organic peroxides for crosslinking a polyolefin elastomer

Info

Publication number: EP3724263A1
Application number: EP18842633.2A
Authority: EP
Inventors: Jean-Pierre Disson; Chao Lu
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2017-12-15
Filing date: 2018-12-14
Publication date: 2020-10-21
Also published as: CN111479862B; KR20200096623A; US20200385545A1; FR3075210B1; FR3075210A1; WO2019115975A1; JP2024028717A; CN111479862A; JP2021507024A

Abstract

The present invention concerns the use of a mixture of organic peroxides for crosslinking a polyolefin elastomer (POE), in particular intended to be used in photovoltaic applications. The invention also relates to a crosslinkable composition comprising at least one polyolefin elastomer (POE) and at least one mixture of organic peroxides. The present invention also concerns a method for preparing a material made from polyolefin elastomer (POE), preferably an encapsulating material or a sealing agent, in particular for photovoltaic cells, comprising a step of crosslinking a crosslinkable composition as defined previously.

Description

Use of a mixture of organic peroxides for the crosslinking of a polyolefin elastomer

The present invention relates to the use of a mixture of organic peroxides, as defined hereinafter, for the crosslinking of polyolefin elastomer (POE), preferably of a copolymer of ethylene and at least one alpha-olefin , in particular for use in photovoltaic applications.

The invention also relates to a crosslinkable composition comprising at least one elastomeric polyolefin (POE), preferably a copolymer of ethylene and at least one alpha-olefin, and at least one mixture of organic peroxides as defined below.

The present invention also relates to a process for preparing an elastomeric polyolefin (POE) based material, preferably an encapsulating material, in particular photovoltaic cells, comprising a step of crosslinking a crosslinkable composition as defined above. .

The invention also relates to the elastomer polyolefin material, preferably a copolymer of ethylene and at least one alpha-olefin, obtainable by the process previously described and a photovoltaic module comprising such a material.

Photovoltaic modules (also called panels or solar collectors) generally have the role of converting incident solar energy into electrical energy so as to produce electricity in the form of direct current.

A photovoltaic module corresponds in particular to an assembly of photovoltaic cells (also called solar cells), consisting mainly of semiconductors, which are arranged side by side between a first transparent layer forming a front face of the module and a second layer forming a rear face. of the module. The first layer forming the front face of the module is generally made using a solid and transparent glass plate to allow the photovoltaic cells to receive a luminous flux.

The second layer forming the rear face of the module (or support) can be made from a flexible material, for example plastic, or a material of metal or glass. In particular, the front face and the rear face of the module may both be made with a glass plate (the manufacturing process is then called bi-glass process). In addition, this film is generally colored in white with pigments of the titanium oxide type optionally combined with other fillers (calcium carbonate type, talc, silica, etc.), so as to reflect towards the top of the module. light and thus send back to the cells some of the radiation normally lost in the single-glass panels.

In the case of single-glass panels, the second layer forming the rear face of the module is preferably composed of a multilayer assembly composed for example of a thin layer of electrical insulating polymer, such as polyethylene terephthalate (PET) or the polyamide (PA), surmounted by one or more thin layers based on fluorinated polymers, such as polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF), topped with a metal layer, by aluminum example, to protect the module from possible mechanical shocks. In this case, the rear face of the module can thus be made with such a multilayer assembly while the front face of the module is made with a glass plate.

The photovoltaic cells are electrically connected to each other (in series or in parallel) and encapsulated so as to ensure their electrical insulation as well as their protection against external environmental factors, such as humidity, inclement weather such as rain or snow, and ultraviolet radiation. The materials, preferably in the form of films, for encapsulating photovoltaic cells are commonly designed from homopolymers or copolymers of ethylene. More specifically, copolymers of ethylene and vinyl acetate (EVA) are particularly advantageous for performing such encapsulation because they lead to transparent materials that can easily adhere to the substrates of a photovoltaic module while being equipped a high electrical resistivity. For these reasons, EVA resins account for a majority of the current market.

In order to obtain satisfactory thermomechanical properties for this application, in particular in terms of good adhesion properties with respect to the module substrate, creep resistance and resistance to degradation with respect to the weather, it is It is important to cross-link the copolymers of ethylene and vinyl acetate and to obtain a good crosslinking density. Indeed, if the crosslinking density is too low, the material obtained is likely to have, among other things, insufficient tensile strength and rupture, and to flow over time given the high temperatures that can reach the upper faces of the photovoltaic panels. The crosslinking agents typically employed are peroxides such as dicumyl peroxide (DCP), peroxyesters, peroxyketals, peroxycarbonates, dialkyl peroxides, and mixtures thereof. As an example of monoperoxycarbonate, it is already known to use 00-tert-amyl-O-2-ethylhexylmonoperoxycarbonate (TAEC), OO-tert-butyl-O-2-ethylhexylmonoperoxycarbonate (TBEC), OO- tert-isobutyl-O-isopropylmonoperoxycarbonate (TBIC), or 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane for the crosslinking of copolymers of ethylene and vinyl acetate (EVA).

Thus, during the photovoltaic module manufacturing process, the solar cells and their electrical conductors are arranged between two layers (or films) obtained from a composition based on copolymers of ethylene and vinyl acetate and one or more crosslinking agents. Such a manufacturing method comprises a single step of rolling the various layers forming the photovoltaic module at a certain temperature during a given period during which the EVA-based composition is crosslinked. The different layers of the module are thus compressed together and the solar cells are found coated in a transparent material based on EVA.

However, it has been found that under the effect of ultraviolet radiation and moisture, EVA tends to decompose chemically and release acetic acid which accelerates the corrosion of solar cells and causes yellowing or the browning of the material encapsulating the cells. Such a phenomenon can also induce a change in the transmittance of the incident luminous flux in the solar cells, which in the long run decreases their power.

In addition, this lack of yellowing may be accompanied by a degradation of the adhesion properties between the encapsulating material and the various layers of the module leading, on the one hand, to the penetration of water inside the module and on the other hand, the formation of trapped air bubbles between the encapsulating material and the front and / or rear face of the module. The formation of these air bubbles causes swelling between the encapsulating material and the faces of the module, in particular the rear face, thus leaving unsightly traces visible on the surface (traces called snail trails in English). The presence of these bubbles also makes it more difficult for the heat dissipation of the solar cells, which increases their overheating and affects their service life. In other words, the EVA-based materials have the disadvantage of being permeable under moist heat conditions.

In addition, photovoltaic modules manufactured with

LEVA also have the disadvantage of being particularly sensitive to the progressive degradation of the electrical characteristics of the cells due to the presence of parasitic leakage currents. This phenomenon is known as "Potential Induced Degradation" (PID).

In order to overcome the various disadvantages mentioned above, it has already been proposed in the state of the art to use compounds other than EVA for the preparation of materials for encapsulating solar cells. By way of examples, mention may be made especially of polyvinyl butyrate (PVB), silicone rubber or elastomeric polyolefins (POE) which are of interest for obtaining less permeable materials than those prepared with EVA under heat conditions. wet.

More specifically, the use of elastomeric polyolefins proves to be advantageous for preparing materials intended to encapsulate solar cells, since these cells are endowed with a high electrical resistivity while being poorly permeable under humid heat conditions. The elastomeric polyolefins have in particular good performance in photovoltaic modules whose front and rear faces are made using a glass plate.

However, the elastomeric polyolefins are more difficult to crosslink than the copolymers of ethylene and vinyl acetate and this under identical operating conditions in the presence of the same crosslinking agents. More specifically, the crosslinking process of the elastomeric polyolefins may in particular require higher crosslinking temperatures, higher peroxide concentrations and / or longer crosslinking times than those used for the copolymers of ethylene and acetate. of vinyl. This results in a significant loss of productivity for industries using elastomeric polyolefins in replacement of copolymers of ethylene and vinyl acetate.

In order to overcome this difficulty, JP2017-085032 discloses the use of copolymers of ethylene and alpha-olefin in photovoltaic applications which are crosslinked in the presence of tert-amyl peroxy isopropyl monocarbonate (TAIC). The use of such a crosslinking agent makes it possible to obtain a satisfactory speed and a crosslinking density comparable to those obtained for the copolymers of ethylene and alpha-olefin under similar operating conditions.

However, tert-amyl peroxy isopropyl monocarbonate (TAIC) has the risk of causing premature crosslinking of elastomeric polyolefins, especially in the sheath or at the top of the extruder, before the rolling step of the various layers serving the manufacture of the photovoltaic module is implemented. This phenomenon of premature crosslinking (also called roasting) has the consequence of causing the formation of gel particles in the mass of the mixture which can induce a number of irregularities (inhomogeneity, surface roughness) of the encapsulant material ultimately affecting the appearance and properties of photovoltaic modules. In addition, excessive roasting can lead to the total stop of the extrusion operation thus slowing the productivity of the material.

In other words, the roasting phenomenon is likely to affect both the final properties of the photovoltaic modules and their productivity.

Thus one of the objectives of the present invention is to implement compounds having good crosslinking properties of elastomeric polyolefins, in particular by conferring a satisfactory speed and crosslinking density, in order to obtain a material with thermomechanical properties. adapted to the desired applications, while minimizing the risk of premature crosslinking (or roasting) may affect the productivity and the final properties of said material.

In other words, there is a real need to provide compounds capable of efficiently crosslinking elastomeric polyolefins under similar operating conditions as those used for copolymers of ethylene and vinyl acetate while minimizing the risks of toasting or premature crosslinking.

In view of the foregoing, the object of the invention is more particularly to propose a material intended for encapsulation, preferably solar cells in photovoltaic modules, having not only a high electrical resistivity but also a lower permeability under moist heat conditions than that of a material obtained from copolymers of ethylene and vinyl acetate.

The present invention therefore particularly relates to the use for the crosslinking of an elastomeric polyolefin of a composition comprising:

at least one monoperoxycarbonate corresponding to the formula

(I):

Formula (I) in which R 1 represents an alkyl radical comprising a number of carbon atoms of less than or equal to 6 and R ₂ represents an alkyl radical,

at least one monoperoxycarbonate, corresponding to the following formula (II):

R ₂ - O - O - c - O - R ₁

O

(P)

Formula (II) in which R 1 represents an alkyl radical comprising a number of carbon atoms greater than or equal to 7 and R ₂ represents an alkyl radical.

Preferably, said composition comprises strictly less than 0.4% by weight of a tertiary alkyl hydroperoxide calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and of monoperoxycarbonate of formula (II) . The term "strictly less than 0.4%", from 0 to 0.4% by weight, the 0% terminal being included and the 0.4% terminal being excluded.

Preferably, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated with respect to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and monoperoxycarbonate of formula (II).

Preferably, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of the total content of monoperoxycarbonate of the composition. Even more preferentially, said composition is free of a tert-alkyl hydroperoxide.

In other words, the invention relates to the use of a mixture of at least two different monoperoxycarbonates corresponding respectively to formulas (I) and (II) for the crosslinking of an elastomeric polyolefin, preferably a copolymer of ethylene and at least one alpha-olefin; the mixture containing strictly less than 0.4% dialkyl hydroperoxide calculated relative to 100 parts by weight of the mixture.

The composition according to the invention thus has the advantage of leading to a satisfactory speed and a crosslinking density while minimizing the risks of premature roasting or crosslinking likely to affect the productivity and the final properties of the material obtained.

In other words, the composition according to the invention makes it possible to increase the resistance time to roasting without impacting on the overall rate of crosslinking and the crosslinking density of the elastomeric polyolefins.

More particularly, the composition according to the invention makes it possible in particular to retain the good crosslinking properties obtained with tert-amyl peroxy isopropyl monocarbonate while reducing the risks of premature crosslinking.

Furthermore, the composition according to the invention makes it possible to effectively crosslink elastomeric polyolefins, preferably copolymers of ethylene and at least one alpha-olefin, under operating conditions similar to those used for ethylene copolymers. and vinyl acetate. The invention also relates to a crosslinkable composition comprising at least one elastomeric polyolefin (preferably a copolymer of ethylene and at least one alpha-olefin), at least one monoperoxycarbonate corresponding to formula (I), such as described above, and at least one monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), corresponding to formula (II) as described above.

Preferably, said composition comprises strictly less than 0.4% by weight of a tertiary alkyl hydroperoxide calculated relative to 100 parts by weight of the monoperoxycarbonate mixture of formula (I) and of monoperoxycarbonate of formula (II). The term "strictly less than 0.4%", from 0 to 0.4% by weight, the 0% terminal being included and the 0.4% terminal being excluded.

Preferably, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and monoperoxycarbonate of formula (II). Preferably, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of the total content of monoperoxycarbonate of the composition. More preferably, said composition is free of tert-alkyl hydroperoxide.

The crosslinkable composition according to the invention makes it possible to lead to a material, in particular an encapsulating or sealing material, preferably solar cells, having thermomechanical properties adapted to the desired applications, with a high productivity.

The crosslinkable composition according to the invention thus has the advantage of being crosslinked during a method of manufacturing a photovoltaic module. Furthermore, the present invention also relates to a method for manufacturing a material comprising a step of crosslinking a crosslinkable composition as defined above.

The method according to the invention has the advantage of leading to a material having good thermomechanical properties and whose possible structural asperities are minimized.

Similarly, another object of the invention relates to the material comprising at least one elastomeric polyolefin (preferably a copolymer of ethylene and at least one alpha-olefin), which can be obtained by the process previously described.

The material has the advantage of having good electrical resistivity and being less permeable under moist heat conditions than materials obtained from copolymers of ethylene and vinyl acetate.

In addition, the material does not exhibit any (or few) marked surface defects because of its resistance to roasting.

The material obtained is preferably a material for encapsulating solar cells.

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

The photovoltaic module has improved properties due to the presence of the encapsulating material.

Other characteristics and advantages of the invention will emerge more clearly on reading the description and examples which follow.

In what follows, and unless otherwise indicated, the boundaries of a domain of values are included in this field.

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

use According to the present invention, the composition as described above makes it possible to crosslink the elastomeric polyolefins, preferably of a copolymer of ethylene and at least one alpha-olefin.

By "polyolefin" is meant in the sense of the present invention a polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc.

By "derivative of" is meant in the sense of the present invention that the units of the main chain of the polymer and / or adjacent chains (or pendant chains) of the polymer result from the polymerization or copolymerization of the monomers from which the polymer is manufactured.

For the purposes of the present invention, the term "elastomeric polyolefin" (POE) is understood to mean an elastomeric polymer derived from an olefin, for example ethylene, propylene, butene, hexene, etc.

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

Advantageously, the elastomeric polyolefins according to the present invention are derived from ethylene. In other words, the elastomeric polyolefins preferably comprise at least one unit derived from ethylene.

Preferably, the elastomeric polyolefins according to the present invention further comprise at least one alpha-olefin.

Preferably, the elastomeric polyolefins comprise a content of at least 15% by weight of alpha-olefin, preferably at least 20% by weight and even more preferably at least 25% by weight, calculated with respect to weight. total of the polymer.

Preferably, the elastomeric polyolefins comprise an alpha-olefin content of less than 50% by weight, preferentially less than 45% by weight, and even more preferably less than 35% by weight, calculated on the total weight of the polymer.

Thus, the elastomeric polyolefins may comprise an alpha-olefin content ranging from 15% to 50% by weight, preferably from 15% to 45% by weight, more preferably from 15% to 35% by weight, more preferably from 20% to 35% by weight. % to 35% by weight, calculated on the total weight of the polymer.

The alpha-olefin content within the polymer can be measured by carbon 13 nuclear magnetic resonance spectroscopy (NMR) according to the protocol described by Randall (Rev. Macromol Chem Phys., C29 (2 and 3)).

The alpha-olefin is preferably a linear, branched or cyclic C ₃ -C ₂₀ alpha-olefin.

Preferably, the alpha-olefin is linear or branched C ₃ -C ₂₀ .

Preferably, the C ₃ -C ₂₀ alpha-olefin is selected from the group consisting of propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-propenyl decene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene.

The alpha-olefin may also contain a cyclic structure, for example cyclohexane or cyclopentane, resulting in an alpha-olefin such as 3-cyclohexyl-1-propene (allylcyclohexane) and vinyl cyclohexane.

Certain cyclic olefins, such as norbornene and the corresponding olefins, are considered as alpha-olefins within the meaning of the present invention and may be used in place of the alpha-olefins described above.

Advantageously, the elastomeric polyolefins are copolymers of ethylene and alpha-olefin, especially a linear or branched C ₃ -C ₂₀ alpha-olefin.

Advantageously, the elastomeric polyolefins are copolymers of ethylene and at least one alpha-olefin, especially a linear or branched C ₃ -C ₂₀ alpha-olefin. Advantageously, the elastomeric polyolefins are copolymers consisting exclusively of ethylene and at least one alpha-olefin, to the exclusion of any other comonomer. Preferably, the elastomeric polyolefins are chosen from the group consisting of ethylene / propylene copolymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, in particular very low density polyethylene (VLDPE) (for example polyethylene ethylene / 1-hexene sold under the name Flexomer® by Dow Chemical Company), ethylene / 1-octene copolymers, ethylene / styrene copolymers, ethylene / propylene / 1-octene copolymers, ethylene / propylene / copolymers 1-butene, ethylene / 1-butene / 1-octene copolymers and ethylene / 1-butene / styrene copolymers.

Preferred polyolefin copolymers are selected from the group consisting of linear and homogeneously branched ethylene and alpha-olefin copolymers. The substantially linear ethylene copolymers are particularly preferred and are described in particular in US Pat. No. 5,272,236, US Pat. No. 5,278,272 and US Pat.

As examples of linear and homogeneously branched ethylene and alpha-olefin copolymers, mention may be made of the copolymers sold under the name TAFMER® by the company Mitsui Petrochemicals Company Limited, the name EXACT® by the company Exxon Chemical Company, the names AFFINITY® and ENGAGE® by Dow Chemical Company.

The elastomeric polyolefins may also comprise propylene, 1-butene and other alkylene-based copolymers, for example copolymers comprising a majority of units derived from propylene and a minority of units derived from another alpha-olefin ( including ethylene). Examples of polypropylene belonging to the present invention are in particular the polymers sold under the trade name VERSIFY® by Dow Chemical Company and the trade name VISTAMAXX® by the company Exxon Mobil Chemical Company. Preferably, the elastomeric polyolefins according to the invention have a glass transition temperature (Tg) which is less than -35 ° C., preferably less than -40 ° C., more preferably less than -45 ° C. and even more preferentially less than -40 ° C. -50 ° C, measured by differential scanning calorimetry (DSC) in accordance with ASTM procedure D-3418-03.

Preferably, the elastomeric polyolefins have a Melt Flow Index (MFI) of less than 100 g / l 0 minutes, preferably less than 75 g / 10 minutes, more preferably less than 50 g. 10 minutes and even more preferably less than 35 g / 10 minutes.

Advantageously, the elastomeric polyolefins have a melt flow index (MFI) of less than 1 g / 10 minutes, and even more preferably less than 5 g / 10 minutes.

The melt flow index (MFI) of the elastomeric polyolefins is measured in accordance with commonly used methods for characterizing thermoplastic materials to obtain information on the extrudability as well as the possibilities of shaping the material such as those described in ASTM D l 238, NF T5 1-016 or ISO 1133.

The MFI values referred to are determined according to ASTM D 1238 at a temperature of 90 ° C. under a load of 2.16 kg (units expressed in g / 10 minutes).

Preferably, the elastomeric polyolefins have a density of less than 0.9 g / cc, especially less than 0.89 g / cc, preferably less than 0.885 g / cc, even more preferentially less than 0.88 g / cc and even more preferably less than 0.875 g / cc.

Advantageously, the elastomeric polyolefins have a density greater than 0.85 g / cc and even more preferably greater than 0.86 g / cc.

The density of the elastomeric polyolefins is measured according to the procedure described in ASTM D-792. According to the present invention, the composition used to crosslink the elastomeric polyolefins comprises at least one monoperoxycarbonate of formula (I) as described above.

Preferably, in the formula (I), R 1 represents a branched alkyl radical comprising a number of carbon atoms of less than or equal to 6 and R ₂ represents a branched alkyl radical.

Preferably, in formula (I), R 1 and R ₂ are different.

According to formula (I), R 1 is preferably a C ₂ -C ₅ radical. Preferably, R 1 is a C ₃ alkyl radical, in particular a branched C ₃ (isopropyl) radical.

According to formula (I), R ₂ is preferably a C 1 -C 10 alkyl radical, preferably a C ₄ -C ₅ alkyl radical. Preferably, R ₂ is a C ₅ or C ₆ alkyl radical, in particular branched C ₅ (teramyl) or C ₆ (terhexyl).

Advantageously, R 1 is a C ₂ -C ₅ alkyl radical, and R ₂ is a C ₁ -C ₁₀ alkyl radical, especially a C ₄ -C ₅ alkyl radical.

More advantageously, R 1 is a C ₃ alkyl radical and R ₂ is a C ₅ or C ₆ alkyl radical.

Preferably, the monoperoxycarbonate of formula (I) is selected from the group consisting of tert-amyl peroxy isopropyl monocarbonate (TAIC), tert-amyl peroxy n-propyl monocarbonate (TAPC), tert-butyl peroxy isopropyl monocarbonate (TBIC) , tert-octyl peroxy isopropyl monocarbonate (TOIC) and tert-hexyl peroxy isopropyl monocarbonate) (THIC).

Preferably, the monoperoxycarbonate of formula (I) is chosen from the group consisting of tert-amyl peroxy isopropyl monocarbonate (TAIC) and tert-hexyl peroxy isopropyl monocarbonate (THIC).

Preferably, the monoperoxycarbonate of formula (I) corresponds to tert-amyl peroxy isopropyl monocarbonate (TAIC) of the following formula:

Preferably, in formula (II), R 1 represents a branched alkyl radical comprising a number of carbon atoms greater than or equal to 7 and R ₂ represents a branched alkyl radical.

Preferably, in formula (II), R 1 and R ₂ are different.

According to formula (II), R 1 is an alkyl radical comprising a number of carbon atoms greater than or equal to 7, preferably C ₇ -C ₁₀ , more preferably C ₇ -C ₉ . Preferably, R 1 is a C ₈ alkyl radical, in particular a C ₈ branched radical.

According to formula (II), R ₂ is preferably an alkyl radical C ₁ -C ₁₀ , preferably C ₂ -C ₉ , in particular C ₄ -C ₈ . Preferably, R ₂ is a C ₄ or C ₅ alkyl radical, in particular a branched C ₄ or C ₅ radical. More preferably, R ₂ is a C ₄ alkyl radical, in particular a C ₄ branched radical _.

Advantageously, R 1 is a C ₇ -C ₁₀ alkyl radical, in particular a C ₇ -C ₉ alkyl radical, and R ₂ is a C ₁ -C ₁₀ alkyl radical, in particular a C ₂ -C ₉ alkyl radical _, in particular C ₄ -Cs.

Preferably, the monoperoxycarbonate of formula (II) is selected from the group consisting of O-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate (TAEC), O-tert-butyl-0-2 monoperoxycarbonate ( ethylene hexyl) (TBEC), 00-tert-octyl-0-2 (-ethylhexyl) monoperoxycarbonate (TOEC), and 00-tert-hexyl-0-2 (-ethylhexyl) monoperoxycarbonate (THEC).

The monoperoxycarbonates mentioned above and in accordance with the invention are available under the trade name Luperox® or Lupersol® sold by Arkema.

Preferably, the monoperoxycarbonate of formula (II) corresponds to 00-tert-amyl-O- (2-ethyl hexyl) monoperoxycarbonate (TAEC) or 00-tert-butyl-O- (2-ethyl hexyl) monoperoxycarbonate (TBEC) ), and more particularly to 00-tert-butyl-O- (2-ethyl hexyl) monoperoxycarbonate (TBEC). Preferably, the weight ratio between the monoperoxycarbonate of formula (I) and the monoperoxycarbonate of formula (II) varies in the range from 0.1: 99.9 to 80: 20, preferably from 1: 99 to 70: 30. and more preferably from 10: 90 to 60:40.

More preferably, the weight ratio between the monoperoxycarbonate of formula (I) and the monoperoxycarbonate of formula (II) is 60:40.

Preferably, in formula (I), R 1 represents a branched alkyl radical comprising a number of carbon atoms of less than or equal to 6 and R ₂ represents a branched alkyl radical, and, in formula (II), R 1 represents a radical branched alkyl comprising a number of carbon atoms greater than or equal to 7 and R ₂ represents a branched alkyl radical.

Advantageously, the invention relates to the use of tert-amyl peroxy isopropyl monocarbonate (TAIC) and a monoperoxycarbonate of formula (II) chosen from the group consisting of 00-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate. ) (TAEC), 00-tert-butyl-O- (2-ethylhexyl) monoperoxycarbonate (TBEC), 00-tert-octyl-0-2 (-ethylhexyl) monoperoxycarbonate (TOEC), and monoperoxycarbonate of 00 -tert-hexyl-O-2 (-ethylhexyl) (THEC). for the crosslinking of an elastomeric polyolefin.

Preferably, the invention relates to the use of: tert-amyl peroxy isopropyl monocarbonate (TAIC) and 00-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate (TAEC) or 00-tert-butyl-monoperoxycarbonate. 0- (2-ethylhexyl) (TBEC) for crosslinking an elastomeric polyolefin, preferably a copolymer of ethylene and at least one alpha-olefin. Preferably, the invention relates to the use of tert-amyl peroxy isopropyl monocarbonate (TAIC) and O-tert-butyl-O- (2-ethylhexyl) monoperoxycarbonate (TBEC) for the crosslinking of an elastomeric polyolefin. According to these embodiments, the elastomeric polyolefin preferably comprises at least one unit derived from ethylene.

According to these embodiments, the elastomeric polyolefin is preferably selected from the group consisting of copolymers of ethylene and alpha-olefin, especially a linear or branched C3-C20 alpha-olefin.

Preferably, said composition comprises strictly less than 0.4% by weight of a tertiary alkyl hydroperoxide calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and of monoperoxycarbonate of formula (II) .

Preferably, the composition according to the invention does not comprise tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and monoperoxycarbonate of formula (II). Advantageously, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of the total content of monoperoxycarbonate of the composition. Still preferentially,

In particular, the composition according to the invention does not comprise tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated with respect to 100 parts by weight of a mixture consisting of amyl peroxy isopropyl monocarbonate (TAIC) and 00-tert-amyl-O- (2-ethyl hexyl) monoperoxycarbonate (TAEC).

Preferentially, the tert-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), paramentane hydroperoxide (PMHP), 2,5-dimethyl-2,5-dihydroperoxide (2,5-2,5) and mixtures thereof. More particularly, the composition is free of tert-alkyl hydroperoxide.

Crosslinkable composition

As indicated above, the crosslinkable composition comprises:

at least one elastomeric polyolefin (preferably a copolymer of ethylene and at least one alpha-olefin) as described above,

at least one monoperoxycarbonate corresponding to the formula

(I), as previously described, and

at least one monoperoxycarbonate, corresponding to the formula

(II) as previously described;

Preferably, said composition comprises strictly less than 0.4% by weight of a tertiary alkyl hydroperoxide calculated with respect to

100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and monoperoxycarbonate of formula (II).

Preferably, the composition is free of tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and monoperoxycarbonate of formula (II).

Preferably, said composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of the total content of monoperoxycarbonate of the composition.

The monoperoxycarbonates of formulas (I) and (II) are preferably present in the composition in a content of less than or equal to 3 parts by weight per 100 parts by weight of the elastomeric polyolefin. Thus the amount of monoperoxycarbonates of formulas (I) and (II) is preferably less than or equal to 3 parts by weight per 100 parts by weight of the elastomeric polyolefin.

Preferably, the amount of monoperoxycarbonates of formulas (I) and (II) varies in the range from 0.1 to less than 3 parts by weight, preferably from 0.2 to 1.5, more preferably from 0.3. at 1, more preferably from 0.4 to 1, more preferably from 0.4 to 0.7 and most preferably about 0.5 parts by weight, per 100 parts by weight of the elastomeric polyolefin.

Advantageously, the crosslinkable composition comprises an elastomeric polyolefin, tert-amyl peroxy isopropyl monocarbonate (TAIC) and a monoperoxycarbonate of formula (II) chosen from the group consisting of 00-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate. (TAEC), OO-tert-butyl-O- (2-ethylhexyl) monoperoxycarbonate (TBEC), OO-tert-octyl-O-2 (-ethylhexyl) monoperoxycarbonate (TOEC) and OO-tert monoperoxycarbonate -hexyl-O-2-ethylhexyl (THEC).

Preferably, the crosslinkable composition comprises an elastomeric polyolefin, tert-amyl peroxy isopropyl monocarbonate (TAIC) and 00-tert-butyl-O- (2-ethylhexyl) monoperoxycarbonate (TBEC).

Alternatively, the crosslinkable composition preferably comprises an elastomeric polyolefin, tert-amyl peroxy isopropyl monocarbonate (TAIC) and OO-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate (TAEC).

Even more preferably, the elastomeric polyolefin is preferably selected from the group consisting of copolymers of ethylene and alpha-olefin, especially copolymers of ethylene and linear or branched C ₃ -C ₂₀ alpha-olefin.

Preferably, the weight ratio between the monoperoxycarbonate of formula (I) and the monoperoxycarbonate of formula (II) is 60:40.

The crosslinkable composition of the invention may further comprise 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.

The 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 dimethacrylate glycol, polyethylene glycol 200 dimethacrylate, polyethylene glycol 400 dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,1,2-dodecanediol dimethacrylate, 1, 3 glycerol dimethacrylate, diurethane dimethacrylate, trimethylolpropane trimethacrylate, epoxy bisphenol A diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate , tetraethylene glycol diacrylate, d neopentyl glycol ethoxylate acrylate, butanediol diacrylate, hexanediol diacrylate, aliphatic urethane diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, glycerol propoxylate triacrylate, triacrylate aliphatic urethane, trimethylolpropane triacrylate and dipentaerythritol pentaacrylate, triallyl cyanurate (TAC), triallyl isocyanurate, N, N'-m-phenylenedimaleimide, butadiene, chloroprene and isoprene.

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

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.

The main objective of the use of a co-agent in the crosslinkable composition according to the invention is to increase the degree of crosslinking. This co-agent also makes it possible to reduce the emission of residual gas during the decomposition of these same peroxides, and finally to reduce the number of bubbles in the encapsulation material.

Preferably, the weight ratio of monoperoxycarbonates and crosslinking co-agent is in the range of 1:10 to 10: 1, most preferably 1: 3 to 3: 1.

The crosslinkable composition of this invention may further comprise one or more additives such as coupling agents, UV stabilizers, UV absorbers, fillers, plasticizers, flame retardants, antioxidants, dyes, organic pigments. or minerals, and mixtures thereof. Examples of coupling agents are monoalkyl titanates,

(vinyl) trichlorosilanes and (vinyl) trialkoxysilanes. They may represent from 0.01 to 5% by weight relative to the weight of ethylene polymer.

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

Inorganic fillers such as silicon dioxide, alumina, talc, calcium carbonate can be added to increase strength, although nanoscale clays are preferred because of the transparency they confer. Organic or inorganic pigments may also be added to color the crosslinkable composition. There may be mentioned in particular titanium dioxide, to obtain a white color, particularly useful when the composition is used to make a film used on the back side of the photovoltaic panels.

Examples of plasticizers are paraffinic or aromatic mineral oils, phthalates, azelates, adipates and the like.

Antioxidants may be phenolic antioxidants, phosphate or sulfur. Alternatively, quinolines such as 1,2-dihydro-2,2,4-trimethylquinoline can be used as an antioxidant.

According to a preferred embodiment, the total amount of peroxide in the crosslinkable composition is less than 3 parts by weight per 100 parts by weight of the elastomeric polyolefin, more preferably less than 1.5 parts by weight per 100 parts by weight of the elastomeric polyolefin.

More preferably, the crosslinkable composition consists of an elastomeric polyolefin as described above, a monoperoxycarbonate of formula (I) and a monoperoxycarbonate of formula (II) as described above, and optionally at least one of following additives: coupling agent, UV stabilizer, UV absorber, filler, plasticizer, flame retardant, antioxidant, dye, co-agent and mixtures thereof.

Preferably, the crosslinkable composition according to the invention comprises an elastomeric polyolefin as described above, a monoperoxycarbonate of formula (I) and a monoperoxycarbonate of formula (II) as described above, a coupling agent and a co-polymer. agent.

Use of the monoperoxycarbonate of formula (II) The invention also relates to the use of a monoperoxycarbonate of formula (II), as described above, for reducing the risks of premature crosslinking of a composition comprising at least one elastomeric polyolefin (preferably an ethylene copolymer). and at least one alpha-olefin), as described above, and at least one monoperoxycarbonate of formula (I) as defined above.

In other words, the monoperoxycarbonate of formula (II) makes it possible to increase the toasting time of a composition comprising at least one elastomeric polyolefin (preferably a copolymer of ethylene and at least one alpha-olefin) and at least one monoperoxycarbonate of formula (I).

Process for preparing the crosslinkable composition

The present invention also relates to a process for preparing the crosslinkable composition as defined above, comprising a step of mixing at least one elastomeric polyolefin (preferably at least one copolymer of ethylene and at least one less an alpha-olefin) as described above, at least one monoperoxycarbonate of formula (I) as described above, and at least one monoperoxycarbonate, different from the monoperoxycarbonate of formula (I), corresponding to formula (II) as as previously described.

Advantageously, the mixing step may be carried out in conventional devices such as continuous mixers and extruder mixers, preferably at a temperature below the degradation temperature of the monoperoxycarbonates of the invention.

Method of manufacturing a material from the crosslinkable composition The invention also relates to a method of manufacturing a material comprising (a) at least one step of crosslinking (or curing) of a crosslinkable composition as defined above.

Preferably, the material comprises an elastomeric polyolefin comprising at least one unit derived from ethylene.

The material is especially selected from the group consisting of encapsulating material, in particular solar cell encapsulating material, wire and cable insulation, hoses and hoses (including hoses for radiators). automotive, drinking water and underfloor heating, for example), roller coatings, rotary moldings, cellular articles, and shoe soles.

Advantageously, the material is a material for encapsulating solar cells.

Preferably, the crosslinking (or curing) step consists of a rolling step.

Preferably, the crosslinking step (a) is carried out at a temperature ranging from 130 to 250 ° C, preferably from 130 to 180 ° C, more preferably from 140 to 165 ° C.

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

Preferably, said method comprises a preceding and / or simultaneous step (a ') in the crosslinking step (a) chosen from the group consisting of molding, extrusion and injection of the composition as defined herein. -above. When the material is a solar cell encapsulation material, said step is preferably an extrusion step.

Step (a ') may be conducted to obtain a sheet having a thickness of 50 to 2000 μm, preferably 100 to 1000 μm, for example. Said step (a ') may be conducted with a T-die extruder or alternatively a twin-screw extruder coupled to a two-roll mill.

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

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

In a particular embodiment, steps (a ') and (a) are conducted in a single step.

Method of manufacturing a photovoltaic module

According to one embodiment, the present invention relates to a method of manufacturing a photovoltaic module comprising:

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

A first transparent layer forming the front face of a photovoltaic module,

A layer obtained from the crosslinkable composition according to the invention,

A plurality of solar cells arranged side by side and electrically connected to each other,

A layer obtained from the crosslinkable composition according to the invention,

A second layer or a multilayer assembly forming the rear face (or support) of the module

(ii) at least one step of pressing the laminated layers together during step (i). The first layer forming the front face of the photovoltaic module may be a glass sheet or a sheet of poly (methyl methacrylate) (PMMA). The second layer forming the rear face of the module may be a thin glass sheet or a sheet of poly (methyl methacrylate) (PMMA).

Alternatively, the multilayer assembly forming the rear face of the module is composed of an electrically insulating polymer film, such as polyethylene terephthalate (PET) or polyamide (PA), surmounted by one or more films with base of fluorinated polymers, such as polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF), capable (s) to be surmount (s) of a metal film, for example aluminum.

In a variant, the multilayer assembly forming the rear face of the module is composed of a glass sheet surmounted by a material comprising an elastomeric polyolefin that can be obtained by the process described above.

The solar cells are preferably made of crystalline silicon or organic photovoltaic substances.

Preferably, the layers obtained from the crosslinkable composition according to the invention are sheets.

The pressing step can be carried out by conventional techniques, under heating and / or under vacuum, for example at a temperature of 130 to 250 ° C, preferably 130 to 180 ° C, more preferably 140 to 165 ° C. C under vacuum, during a curing time which can vary in the range of 8 to 30 minutes, for example from 8 to 25 minutes. The composition of the invention may be crosslinked during this pressing step or thereafter.

Preferably, the method comprises a single simultaneous step of pressing and curing (or crosslinking).

Elastomer polyolefin material

Similarly, another object of the invention relates to a material comprising at least one elastomeric polyolefin (preferably a copolymer of ethylene and at least one alpha-olefin) which can be obtained by the process previously described. The obtained material is preferably selected from the group consisting of encapsulating material, in particular solar cell encapsulating material, wire and cable insulation, hoses and hoses (including hoses for automotive radiators, potable water and underfloor heating, for example), roller coatings, rotary moldings and cellular articles, and shoe soles.

Advantageously, the material is an encapsulation material, and even more preferably a material for encapsulating solar cells.

Still advantageously, the encapsulating material is a transparent film disposed 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 disposed between the panel glass forming the rear face of the module (lower glass panel) and solar cells in the case of bi-glass processes.

Thus, the material is preferably used in a method of manufacturing a photovoltaic module, in particular in a bi-glass process.

More preferably, the material comprising an elastomeric polyolefin is a film, in particular an ethylene polymer film, in particular linear and homogeneously branched ethylene and alpha-olefin copolymers.

The material according to the invention has an improved crosslinking density and a marked decrease or absence of roasting problems. This makes it possible to obtain films which have no surface defects and which have good resistivity. Photovoltaic module

The invention also relates to a photovoltaic module comprising at least one solar cell encapsulation material as described above. In particular, the photovoltaic module according to the invention comprises at least:

A first transparent layer forming the front face of the photovoltaic module and intended to receive a luminous flux,

An encapsulating material, as described above, a plurality of solar cells arranged side by side and electrically connected to each other,

A second layer or a multilayer assembly forming the rear 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 the multilayer assembly.

The following examples serve to illustrate the invention without being limiting in nature.

Example:

Example 1

The following compositions were prepared by mixing:

an elastomeric polyolefin (KST340T from Japan Polyethylene Corporation, MFI 12-16 g / 10 min with a 5 kg load, melting point of 55 ~ 70 ° C., measured by DSC), tert-amyl peroxy isopropyl monocarbonate (Luperox® TAIC marketed) by Arkema),

the same elastomer polyolefin, but with OO-tert-butyl-O-isopropyl monoperoxycarbonate (Luperox® TBIC marketed by Arkema),

the same elastomer polyolefin, but with tert-amyl peroxy isopropyl monocarbonate (TAIC) and monoperoxycarbonate of 00-tert-amyl-O- (2-ethylhexyl) (TAEC) in a weight ratio of 60:40,

the same elastomer polyolefin, but with tert-amyl peroxy isopropyl monocarbonate (TAIC) and 00-tert-butyl-O- (2-ethylhexyl) monoperoxycarbonate (TBEC) in a weight ratio of 60:40,

the same polyolefin elastomer, but with 00-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate (TAEC), the same elastomeric polyolefin, but with 00-tert-butyl-O- (2-ethylhexyl) t-monoperoxycarbonate ) (TBEC).

The compositions were thus prepared in a Haake internal mixer at a temperature of 35 ° C. for a period of 12 minutes, using a rotational speed of 50 rpm. The polymer blend is then passed through an open mill set at a temperature of 50 ° C to produce sheets about 2 mm thick.

Samples of about 2 to 3 grams of the above compositions are deposited in a plate on a moving die rheometer. (MDR) provided by GOTECH, which is able to measure the curing properties of samples and includes software to analyze the results. Each of the samples is placed in a temperature-controlled cavity between two dies, the lowest of which oscillates so as to apply a stress or cyclical deformation to the sample while the upper die is connected to a torque sensor to measure the response of the sample. torque of the sample to deformation.

Rigidity is continuously recorded as a function of time. The stiffness of the sample increases as vulcanization occurs.

This device is able to provide, among others, calculated values of ML (minimum torque), MH (maximum torque, which when reached also defines the time required to reach the hardening state), tc 0 (time before 10% curing state) and tc90 (time before 90% curing state) as defined by international standards (ASTM D5289 and ISO 6502).

The MDR is operated at a temperature of 115 ° C and 145 ° C with an oscillation amplitude (degree of deformation) of 0.5 ° applied to the sample for 30 minutes. The roasting time is defined as the time required to reach 10% of the total cure, i.e., tc l O.

This test is carried out on the following samples, in which the amounts of monoperoxycarbonate are indicated in parts per hundred parts of POE (phr):

The use of TBIC leads to a rate of crosslinking POE too slow since the crosslinking time (tc90) is 20 minutes which is not satisfactory industrially.

The use of TAIC makes it possible to increase the rate of crosslinking of POE relative to TBIC and to slightly improve the crosslinking density (MH-ML). However, the roasting time (tc l O) is problematic and can lead to risks from an industrial point of view, in particular by creating roughness at the surface of the encapsulating material.

The use of TBEC leads to excessive polymer cross-linking times (tc90). In addition, the use of TAEC and TBEC lead to insufficient crosslinking density (MH-ML).

The use of a mixture of TAIC and TAEC makes it possible both to accelerate the crosslinking of the POE compared to the formulation containing only TBIC, or TBEC (tc90), to maintain a good crosslinking density, better than with the TAEC or the TBEC, while guarding against the risk of premature crosslinking by increasing the roasting time (tc l O) compared to the formulation containing only the TAIC.

Similarly, the use of a mixture of TAIC and TBEC makes it possible both to accelerate the crosslinking of the POE compared to the formulation containing only TBIC or TBEC (tc90), to maintain a good crosslinking density while by guarding against the risk of premature crosslinking by extending the roasting time (tc l O) compared to the formulation containing only the TAIC.

Claims

1. Use for crosslinking an elastomeric polyolefin of a composition comprising:

at least one monoperoxycarbonate corresponding to the formula

(I):

R _2- o- o- c- O- R ₁

O

(I)

Formula (I) in which R 1 represents an alkyl radical comprising a number of carbon atoms of less than or equal to 6 and R ₂ represents an alkyl radical, and at least one monoperoxy carbonate, corresponding to the formula

(II):

R _2- o- o- c- o- R ₁

O

(P)

2. Use according to claim 1, characterized in that the composition comprises strictly less than 0.4% by weight of a tert-alkyl hydroperoxide calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I ) and monoperoxycarbonate of formula (II).

3. Use according to claim 1 or 2, characterized in that the polyolefin elastomer is a copolymer of ethylene and at least one alpha-olefin, preferably a linear, branched or cyclic C ₃ -C ₂₀ alpha-olefin.

4. Use according to any one of claims 1 to 3, characterized in that the elastomeric polyolefin is selected from the group consisting of ethylene / propylene copolymers, copolymers of ethylene / 1-butene, ethylene / 1-hexene copolymers, ethylene / 1-octene copolymers, ethylene / styrene copolymers, ethylene / propylene / 1-octene copolymers, ethylene / propylene / 1 copolymers butene, ethylene / 1-butene / 1-octene copolymers and ethylene / 1-butene / styrene copolymers.

5. Use according to any one of claims 1 to 4, characterized in that the elastomeric polyolefin is selected from the group consisting of copolymers of ethylene and alpha-olefin linear and branched homogeneously.

6. Use according to any one of the preceding claims, characterized in that, in the formula (I), R1 is a C2-C5 alkyl radical, more preferably is a C3 alkyl radical.

7. Use according to any one of the preceding claims, characterized in that, in the formula (I), R ₂ is a C ₁ -C ₁₀ alkyl radical, preferably a C ₄ -C ₅ alkyl radical, preferentially an alkyl radical. C ₅ or C _6, more preferably is a C ₅ alkyl radical.

8. Use according to any one of the preceding claims, characterized in that the monoperoxycarbonate of formula (I) is selected 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), preferentially is tert-amyl peroxy isopropyl monocarbonate (TAIC).

9. Use according to any one of the preceding claims, characterized in that, in the formula (II), R 1 is a C ₇ -C ₁₀ alkyl radical, more preferably C ₇ -C ₉ , still more preferably is a radical C ₈ alkyl.

10. Use according to any one of the preceding claims, characterized in that, in formula (II), R ₂ is a C 1 -C 10 alkyl radical, preferably a C ₂ -C ₉ alkyl radical, in particular C ₄ -C ₈ , more preferably is a C ₄ or C ₅ alkyl radical, more preferably is a C ₄ alkyl radical.

1 1. Use according to any one of the preceding claims, characterized in that the monoperoxycarbonate of formula (II) is chosen from the group consisting of 00-tert-amyl-O- (2-ethylhexyl) monoperoxycarbonate (TAEC), monoperoxycarbonate 00-tert-butyl-O-2-ethylhexyl (TBEC), 00-tert-octyl-0-2 (-ethylhexyl) monoperoxycarbonate (TOEC) and 00-tert-hexyl-0-2 monoperoxycarbonate ( ethylhexyl) (THEC).

12. Use according to any one of the preceding claims, characterized in that the weight ratio between the monoperoxycarbonate of formula (I) and the monoperoxycarbonate of formula (II) varies in the range from 0, 1: 99.9 to 80 : 20, preferably from 1: 99 to 70: 30 and more preferably from 10: 90 to 60:40.

13. Crosslinkable composition comprising:

at least one elastomeric polyolefin as defined according to any one of claims 1 to 5, is preferably a copolymer of ethylene and at least one alpha-olefin as defined according to any one of claims 3 to 5; ,

at least one monoperoxycarbonate of formula (I) as defined according to any one of claims 1 or 6 to 8,

at least one monoperoxycarbonate of formula (II) as defined according to any one of claims 1 or 9 to 11;

the composition preferably comprising strictly less than 0.4% by weight of a tertiary alkyl hydroperoxide calculated relative to 100 parts by weight of the mixture of monoperoxycarbonate of formula (I) and of monoperoxycarbonate of formula (II).

Crosslinkable composition according to claim 13, characterized in that the content of monoperoxycarbonates of formulas (I) and (II) is less than or equal to 3 parts by weight per 100 parts by weight of the elastomeric polyolefin.

15. Crosslinkable composition according to claim 13 or 14, characterized in that it further comprises at least one co-agent other than an organic peroxide, preferably chosen from the group consisting of triallyl cyanurate, triallyl isocyanurate, N, N'-m-phenylenedimaleimide, triallyl trimellitate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, preferably selected from the group consisting of triallyl cyanurate , triallyl isocyanurate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, and even more preferably is triallyl isocyanurate.

16. Use according to any one of claims 1 and 3 to 12 or composition according to any one of claims 13 to 15, characterized in that the composition is free of a tert-alkyl hydroperoxide present in a content ranging from 0.4 to less than 4% by weight calculated relative to 100 parts by weight of a mixture of monoperoxycarbonate of formula (I) and of monoperoxycarbonate of formula (II), in particular calculated with respect to 100 parts by weight of total monoperoxycarbonate content of the composition.

17. Use according to any one of claims 1 and 3 to 12 or composition according to any one of claims 13 to 15, characterized in that the composition is free of a tert-alkyl hydroperoxide.

18. A method of manufacturing a material comprising (a) at least one step of crosslinking a crosslinkable composition as defined according to any one of claims 13 to 17.

The method according to claim 18, characterized in that the material is selected from the group consisting of encapsulating material, in particular solar cell encapsulating material, wire and cable insulation, pipes and coils. flexible hoses, roller coatings, rotary moldings, honeycomb articles, and shoe soles.

20. The method of claim 18 or 19, characterized in that the crosslinking step (a) is carried out at a temperature ranging from 130 to 250 ° C, preferably from 130 to 180 ° C, more preferably from 140 to 65 ° C.

21. Process according to any one of claims 18 to 20, characterized in that it comprises an earlier and / or simultaneous step (a ') in step (a) chosen from the group consisting of molding, extrusion and injection of the crosslinkable composition as defined in any one of claims 13 to 17.

22. Material comprising at least one elastomeric polyolefin obtainable by the process as defined in any one of claims 18 to 21.

23. A method of manufacturing a photovoltaic module comprising:

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

A first transparent layer forming the front face of a photovoltaic module,

A layer obtained from the crosslinkable composition as defined according to any one of claims 13 to 17,

(ii) at least one step of pressing the laminated layers together during step (i).

24. Photovoltaic module comprising a solar cell encapsulation material as defined in claim 23.