Field of the invention
5 The present invention relates to the use of a specific peroxide, and
also to a mixture of peroxides including this specific peroxide, for the
crosslinking of an ethylene homopolymer or copolymer and in particular the
ethylene-vinyl acetate (EVA) copolymer or a mixture of EVA with another
ethylene homopolymer or copolymer. The present invention also relates to a
10 crosslinkable composition comprising an ethylene homopolymer or copolymer
and in particular the ethylene-vinyl acetate (EVA) copolymer and this specific
peroxide or the abovementioned mixture of peroxides. The present invention
also relates to a process for crosslinking ethylene homopolymer or copolymer
and in particular the ethylene-vinyl acetate (EVA) copolymer.
15
Prior art
It is known practice to crosslink ethylene homopolymers or
copolymers and in particular the ethylene-vinyl acetate (EVA) copolymer using
the latter in the presence of free-radical-initiating peroxides such as 0,0-tert-
20 butyl 0-(2-ethylhexyl) monoperoxycarbonate. This peroxide 0,0-tert-butyl 0-
(2-ethylhexyl) monoperoxycarbonate is manufactured and sold by the Applicant
under the name Luperox® TBEC.
In certain applications, especially in the production of films
encapsulating electrical components of photovoltaic modules (solar panels), it
25 is absolutely essential for the crosslinked film to offer maximum electricalal
resistivity in order to totally insulate the electrical circuits from the environment.
p !I
wo 2016/012718 2 PCT /FR20 15/052016
In one such application (photovoltaic module encapsulators), EVA
is very commonly used and represents a major proportion of the market at the
present time. The EVA is necessarily crosslinked so that it in particular acquires
the satisfactory thermomechanical properties for this application. Specifically, it
5 is important, in a process for the crosslinking of an ethylene-vinyl acetate (EVA)
copolymer, to conserve good crosslinking density. The reason for this is that
the crosslinking density is an indication of the mechanical properties of the
finished product. Thus, if the crosslinking density is too low, the finished
product may be characterized by mediocre or even insufficient breaking
I 0 strength or tear strength.
Now, the crosslinking of EVA with 0,0-tert-butyl 0-(2-ethylhexyl)
monoperoxycarbonate, conventionally performed at the present time, has the
consequence that the crosslinked polymer has unsatisfactory electricalal
insulation properties.
15 Moreover, the crosslinking times, especially for EVA, obtained via
such processes using 0,0-tert-butyl 0-(2-ethylhexyl) monoperoxycarbonate,
are relatively long. This results in a loss of production efficiency for industries
transforming these elastomers into finished products.
Finally, the amount of peroxide required for this crosslinking is an
20 important factor, not only with regard to the cost of the peroxide per se, but also
due to the degradation products necessarily resulting from such a crosslinking
process.
Taking into co'nsideration in particular all the abovementioned
characteristics and the drawbacks or weaknesses intrinsic to 0,0-tert-butyl 0-
25 (2-ethylhexyl) monoperoxycarbonate as a crosslinking agent for crosslinkable
compositions of elastomeric polymers such as ethylene-vinyl acetate (EVA)
copolymers, there is a real need to find a replacement crosslinking agent, alone
or as a mixture.
5
10
wo 2016/012718 3 PCT /FR20 15/0520 16
US 3 344 126, JP 20 1206 9866, WO 2011/020 760 and WO 2011/067
505 are also known, which all disclose the use of a particular peroxide, 0,0-
tert-butyl 0-isopropyl monoperoxycarbonate (TBIC), for the crosslinking of
ethylene polymer or copolymer.
Admittedly, its efficiency is advantageous, but it has been discovered by
the Applicant that by choosing to combine it with another peroxide of a
particular type, in a quite specific ratio, entirely noteworthy synergism takes
place.
Brief description of the invention
The Applicant has now discovered, surprisingly, that by using a
peroxide of the same family as 0,0-tert-butyl 0-(2-ethylhexyl)
monoperoxycarbonate in combination with a specific organic peroxide selected
15 from TBEC (0,0-tert-butyl 0-2-ethylhexyl monoperoxycarbonate) or TAEC
(0,0-tert-amyl 0-2-ethylhexyl monoperoxycarbonate), the drawbacks of the
latter are overcome and that, in addition, very significant improvements are
achieved regarding certain additional characteristics.
This result is all the more surprising since the crosslinking agent
20 has only one branch R, unlike the peroxide 0,0-tert-butyl 0-(2-ethylhexyl)
monoperoxycarbonate conventionally used, i.e. the branch R presented below:
25
CH3 0
I II
CH3-c-oo-c-o-R
I
CH2
I
CH3
TBEC: R = 2-ethylhexyl
TBIC: R = isopropyl
T AEC: R = 2-ethylhexyl
TA-IPC: R =isopropyl
wo 2016/012718 4 PCT /FR20 15/052016
The peroxide discovered by the Applicant for the particular
application of the crosslinking of polymers including EVA is 0,0-tert-butyl 0-
5 isopropyl monoperoxycarbonate, and as such the abovementioned group R is
the following:
CH3
{H I = isopropyl
CH3
In the case of 0,0-tert-butyl 0-(2-ethylhexyl)
10 monoperoxycarbonate, the radical R is as follows:
CHz-CH3
1
I = 2-ethylhexyl
CH2-CH-(CH2)3-CHJ L. --------'
It was not at all obvious to a person skilled in the art to envisage
that two peroxides that are so structurally similar could have, in the crosslinking
15 of functional polymers and in particular EVA, such different properties/qualities,
in favour of 0,0-tert-butyl 0-isopropyl monoperoxycarbonate or 0,0-tert-amyl
0-isopropyl monoperoxycarbonate.
Thus, the present invention relates to peroxide(s) for the
20 crosslinking of at least one polymer, the said polymer consisting of an ethylene
homopolymer or copolymer and in particular the ethylene-vinyl acetate (EVA)
copolymer or a mixture of EVA with another ethylene homopolymer or
copolymer, characterized in that the peroxide comprises 0,0-tert-butyl 0-
isopropyl monoperoxycarbonate (TBIC) or 0,0-tert-amyl 0-isopropyl
25 monoperoxycarbonate (TA-IPC) as well as 0,0-tert-butyl-0-2-ethylhexyl
monoperoxycarbonate (TBEC) or 0,0-tert-amyl-0-2-ethylhexyl
monoperoxycarbonate (TAEC).
5
wo 2016/012718 5 PCT /FR2015/0520 16
Hereinbelow, the invention is presented in relation with TBIC since
this component is commercially available. However, the experiments were also
conducted with TA-IPC and the Applicant found, for the latter, laboratory results
and properties that are at least as satisfactory as for those with TBIC.
According to a possibility offered by the invention, the only
peroxides used for the crosslinking are the two abovementioned peroxides and
combinations thereof. Thus, in this case, the peroxide consists of a mixture of
0,0-tert-butyl 0-isopropyl monoperoxycarbonate and of 0,0-tert-butyl 0-2-
ethylhexyl monoperoxycarbonate or of 0,0-tert-amyl 0-2-ethylhexyl
10 monoperoxycarbonate ("TBIC + TBEC" or "TBIC + TAEC" mixture), or 0,0-tertamyl
0-isopropyl monoperoxycarbonate and 0,0-tert-butyl 0-2-ethylhexyl
monoperoxycarbonate or 0,0-tert-amyl 0-2-ethylhexyl monoperoxycarbonate
("TA-IPC + TBEC" or "TA-IPC + TAEC" mixture), preferably in a mass ratio of
99%/1% to 1%/99% of these two peroxides forming the said mixture, more
15 preferentially from 40%/60% to 60%/40% of these two peroxides forming the
said mixture, and even more preferentially in a mass ratio of from 45%/55% to
55%/45% of these two peroxides forming the said mixture.
Advantageously, 0,0-tert-butyl 0-isopropyl monoperoxycarbonate
or 0,0-tert-amyl 0-isopropyl monoperoxycarbonate is in dilute form, preferably
20 present in an amount of greater than 50% in the dilution, and even more
preferably present in an amount of greater than 60% in the dilution.
Hereinbelow, for the sake of simplicity, 0,0-tert-butyl 0-(2-
ethylhexyl) monoperoxycarbonate will often be referred to by the abbreviation
TBEC, whereas 0,0-tert-butyl 0-isopropyl monoperoxycarbonate will be
25 referred to by the abbreviation TBIC. It is noted that this simplification of writing
also applies to TA-IPC and TAEC.
Another aspect of the present invention relates to a crosslinkable composition
comprising at least one ethylene-vinyl acetate (EVA) copolymer and at least
ii
I·''
wo 2016/012718 6 PCT /FR20 15/052016
one peroxide, characterized in that the peroxide comprises 0,0-tert-butyl 0-
isopropyl monoperoxycarbonate as well as 0,0-tert-butyl 0-2-ethylhexyl
monoperoxycarbonate or 0,0-tert-amyl 0-2-ethylhexyl monoperoxycarbonate.
Other advantageous characteristics of the invention are specified
5 hereinbelow:
- according to a possibility offered by the invention, the peroxide consists of a
mixture of 0,0-tert-butyl 0-isopropyl monoperoxycarbonate and of 0,0-tertamyl
0-2-ethylhexyl monoperoxycarbonate (TBIC + TBEC) or 0,0-tert-amyl 0-
2-ethylhexyl monoperoxycarbonate (TBIC + TAEC), or 0,0-tert-amyl 0-
10 isopropyl monoperoxycarbonate and 0,0-tert-butyl 0-2-ethylhexyl
monoperoxycarbonate or 0,0-tert-amyl 0-2-ethylhexyl monoperoxycarbonate
("TA-IPC + TBEC" or "TA-IPC + TAEC" mixture), preferably in a ratio of 40% to
60% of these two peroxides forming the said mixture, more preferentially in a
ratio of 45% to 55% of these two peroxides forming the said mixture;
15 -the mixture of peroxides represents between 0.2% and 4% and preferably
between 0.5% and 2.5% of the amount by mass of the polymer present in the
said composition;
-preferably the abovementioned ethylene-vinyl acetate (EVA) copolymer is
present in the said composition in a content ranging from 70% to 99.9% and
20 preferably from 97% to 99% by weight relative to the weight of the composition;
-according to a possibility offered by the invention, as a function of the
applications selected for the crosslinked polymer, the composition also
comprises one or more crosslinking coagents, or promoters. As crosslinking
promoter of multi-substituted aromatic type, mention may be made of
25 divinylbenzene, diisopropenylbenzene, a-methylstyrene, a-methylstyrene dimer
and triallyl trimellitate. As crosslinking promoter based on multi-substituted
methacrylate, mention may be made of ethylene glycol dimethacrylate,
phenylene dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol 200
wo 2016/012718 7 PCT /FR20 1 5/052016
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 and trimethylolpropane trimethacrylate. The crosslinking
5 promoter based on multi-substituted methacrylate is advantageously used, in
particular ethylene glycol dimethacrylate and trimethylolpropane
trimethacrylate. As crosslinking promoter based on multi-substituted acrylate,
mention may be made of bisphenol A epoxy diacrylate, dipropylene glycol
diacrylate, tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate,
I 0 ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol
diacrylate, tetraethylene glycol diacrylate, neopentyl glycol ethoxylate
diacrylate,
diacrylate,
triacrylate,
butanediol diacrylate, hexanediol diacrylate, aliphatic urethane
trimethylolpropane triacrylate, trimethylolpropane ethoxylate
trimethylolpropane propoxylate triacrylate, glycerol propoxylate
I 5 triacrylate, aliphatic urethane triacrylate, trimethylolpropane triacrylate and
dipentaerythritol pentaacrylate. As nitrogenous crosslinking promoter, mention
may be made of triallyl cyanurate (TAC), triallyl isocyanurate (TAlC) and N,N'm-
phenylenedimaleimide. Mention may also be made of monomers multisubstituted
with vinyl groups, butadiene, chloroprene and isoprene. The
20 crosslinking coagents may be used in a content ranging from 0.05% to 30% by
weight and preferentially from 0.1% to 10% by weight relative to the weight of
the composition.
Other functional adjuvants may be used in the composition, such as
one or more plasticizers, adhesion promoters, UV stabilizers and/or UV
25 absorbers, antioxidants, flame retardants, colorants/optical brighteners,
pigments and reinforcing fillers;
- in the latter case, the functional agent is present in the said composition in a
i . I
content ranging from 0.05% to 30% by weight and preferentially from 0.1% to
10% by weight relative to the weight of the composition.
wo 2016/012718 8 PCT/FR2015/052016
It will be noted hereinbelow that the invention is presented, when
there is a mixture of peroxides, with the additional peroxide consisting of 0,0-
tert-butyl 0-2-ethylhexyl monoperoxycarbonate (TBEC), but it is clearly
understood that the Applicant has also tested 0,0-tert-amyl 0-2-ethylhexyl
5 monoperoxycarbonate (TAEC) and that the latter functions at least just as
satisfactorily as TBEC when used as a mixture with TBIC or TA-IPC.
The present invention also relates to a process for manufacturing a
crosslinked polymer film, characterized in that it comprises at least the following
steps:
10 - ao) extrusion in the form of a film of a crosslinkable composition as
15
defined above,
- bo) crosslinking of the said crosslinkable composition after the
said extrusion step ao) for a time of not more than twenty minutes, preferably
less than fifteen minutes.
Description of the attached figures
The description that follows is given purely as a non-limiting
illustration with reference to the attached figures, in which:
-Figure 1 shows the crosslinking density (XL) of an EVA film as a
20 function of the dose for various peroxides;
- Figure 2 shows the (electricalal) resistivity by volume (VR) for
various compositions, from pure EVA (non-crosslinked) up to mixtures of EVA
that has been crosslinked with TBEC and TBIC;
· - Figure 3 shows the change in the VR as a function of the dose of
25 TBIC;
II
5
wo 2016/012718 9 l'CT /FR20 15/052016
- Figure 4 shows the change in the VR as a function of the content
of isododecane (standard hydrocarbon-based solvent for peroxides);
-Figure 5 shows the resistivity by volume of an EVA polymer
crosslinked with TBIC as a function of the crosslinking time;
- Figure 6 shows the change in the VR as a function of the dose of
TBIC.
Detailed description of the invention
As regards both the peroxides and the preferred polymer intended
10 to be crosslinked, namely EVA, all these products are well known to those
skilled in the art, both as regards their manufacture and as regards their
commercial availability.
15
The following additional information regarding these products may
simply be noted.
Ethylene-vinyl acetate (EVA) copolymers that are suitable for use
in 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, 33-45 PV,
33-400, 34-50 PV, by the company Arkema. The vinyl acetate content of the
20 ethylene-vinyl acetate copolymers that are suitable for use in the present
invention may vary: for example, these copolymers may have a low content of
vinyl acetate or a high content of vinyl acetate.
0,0-tert-Butyl 0-isopropyl monoperoxycarbonate is commercially
sold ~specially by the Applicant, under the name Luperox® TBIC. At the present . .
25 time, this peroxide is found in liquid form at concentrations ranging up to 77%,
the solvent being a hydrocarbon, for instance isododecane. The Applicant sells,
for example, this peroxide under the name Luperox® TBIC M75, i.e. at 75% in
5
10
15
wo 2016/012718 10 PCT /FR20 15/052016
isododecane. The fact that this peroxide is not manufactured or sold in pure or
virtually pure form is solely due to safety requirements (linked to its intrinsic
thermo-sensitivity) which are liable to change over time. Hereinbelow, the
examples tested are performed with Luperox® TBIC M75, but
understood that larger amounts of 0,0-tert-butyl
it is clearly
0-isopropyl
monoperoxycarbonate (above 75%) were tested in the laboratory and that the
results presented with this product were validated with different contents (in
particular higher contents of TBIC which are not repeated here in the attached
figures).
0,0-tert-Butyl . 0-(2-ethylhexyl) monoperoxycarbonate is sold
commercially especially by the Applicant under the name Luperox® TBEC. At
the present time, this peroxide is conventionally found in pure (or virtually pure)
form or even in diluted form.
The preparation of the crosslinked polymer according to the
invention is entirely conventional and well known to those skilled in the art. The
only point to be noted lies in the fact that the heating time required for the
crosslinking is reduced herein, and that a smaller amount of peroxide is
necessary to achieve the set objectives, in particular as regards the criterion of
20 resistivity by volume.
In particular (but not exclusively) in the application of the
crosslinked polymer according to the invention to an encapsulator of a
photovoltaic module, the film may comprise one or more functional adjuvants in
25 the composition to a maximum proportion of 30% by weight of the composition
1and will be chosen more particularly from the compounds mentioned below or a
mixture of these compounds.
li
wo 2016/012718 II l'CT /FR20 15/052016
One or more crosslinking coagents, or promoters, may be added to
the composition according to the invention in order to improve the crosslinking
density and kinetics. As crosslinking promoter of multi-substituted aromatic
type, mention may be made of divinylbenzene, diisopropenylbenzene, a-
5 methylstyrene, a-methylstyrene dimer and triallyl trimellitate. As crosslinking
promoter based on multi-substituted methacrylate, mention may be made of
ethylene glycol dimethacrylate, phenylene dimethacrylate, diethylene glycol
dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol
dimethacrylate, polyethylene glycol 200 dimethacrylate, polyethylene glycol 400
I 0 dimethacrylate, 1,3-butanediol dimethacrylate, 1.4-butanediol dimethacrylate,
1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate, 1,3-glycerol
dimethacrylate, diurethane dimethacrylate and trimethylolpropane
trimethacrylate. The crosslinking promoter based on multi-substituted
methacrylate is advantageously used, in particular ethylene glycol
15 dimethacrylate and trimethylolpropane trimethacrylate. As crosslinking
promoter based on multi-substituted acrylate, mention may be made of
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
20 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. As
25 nitrogenous crosslinking promoter, mention may be made of triallyl cyanurate
(TAC), triallyl isocyanurate (TAlC) and N,N'-m-phenylenedimaleimide. Mention
may also be made of monomers multi-substituted with vinyl groups, butadiene,
chloroprene and isoprene.
Plasticizers may also be added to the composition according to the
30 invention in order to facilitate the implementation and to improve the production
efficiency of the process for manufacturing the composition and the structures.
II
5
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Examples that will be mentioned include paraffinic, aromatic or naphthenic
mineral oils which also make it possible to improve the adhesion power of the
composition according to the invention. Plasticizers that may also be mentioned
include phthalates, azelates, adipates and tricresyl phosphate.
Similarly, although not necessary, adhesion promoters may
advantageously be added in order to improve the adhesion power of the
composition when this power must be particularly high. The adhesion promoter
is a non-polymeric ingredient; it may be organic, crystalline, mineral and more
preferentially semi-mineral semi-organic. Among the latter, mention may be
I 0 made of organic silanes or titanates, for instance monoalkyl titanates,
trichlorosilanes and trialkoxysilanes. It may also be envisaged for these
adhesion promoters to be directly grafted onto the first or the second copolymer
via a technique that is well known to those skilled in the art, for example via
reactive extrusion.
15 Since UV radiation is liable to result in slight yellowing of
thermoplastic compositions, UV stabilizers and UV absorbers (these
compounds generally being referred to as anti-UV agents) such as
benzotriazole, benzophenone and other hindered amines, may be added in
certain applications in which such a phenomenon must be avoided. These
20 compounds may be, for example, based on benzophenone or benzotriazole.
They may be added in amounts of less than 10% by mass and preferentially
from 0.1% to 5% by mass relative to the total mass of the composition.
Antioxidants may also be added to limit the yellowing during the
manufacture of the composition, such as phosphorus compounds
25 (phosphonites and/or phosphites) and hindered phenolic compounds. These
antioxidants may be added in amounts of less than 10% by mass and
preferentially from 0.05% to 5% by mass relative to the total mass of the
composition. An antioxidant that is preferred in the context of the present
invention may consist, for example, of (1 ,2--dihydro-2,2,4-trimethylquinoline),
30 also known by the abbreviation TMQ.
wo 2016/012718 13 PCT /FR20 15/052016
Similarly, in certain applications, flame retardants may also be
added to the composition according to the invention. These agents may be
halogenated or non-halogenated. Among the halogenated agents, mention may
be made of brominated products. Non-halogenated agents that may also be
5 used include phosphorus-based additives such as ammonium polyphosphate,
aluminium phosphinates and phosphonates, melamine cyanurates,
pentaerythritol, zeolites, and also mixtures of these agents. The composition
may comprise these agents in proportions typically ranging from 3% to 30%
relative to the total mass of the composition. Dyes or optical brighteners may
I 0 also be added.
Pigments, for instance titanium dioxide or zinc oxide, may also be
added to the composition in proportions generally ranging from 5% to 10%
relative to the total mass of the composition.
Reinforcing fillers such as talc, glass fibres, carbon fibres,
15 montmorillonites, carbon nanotubes or carbon black may also be added to the
composition, in proportions generally ranging from 2.5% to 30% and more
preferentially up to 10%, relative to the total mass of the composition.
20
Materials used for making the test formulations:
TBEC means 0,0-tert-butyl 0-2-ethylhexyl monoperoxycarbonate.
As presented previously, it is provided in the examples illustrating the present
application by Luperox® TBEC manufactured and sold by the Applicant.
TBIC means 0,0-tert-butyl 0-isopropyl monoperoxycarbonate. As
presented previously, it is provided in the examples illustrating the present
25 application by Luperox® TBIC M75, i.e. TBIC is present to 75% in an
isododecane solution. In the various figures, taken from some of the tests
performed by the Applicant, TBIC especially is noted with a variable dilution
index, especially at 40%, 50% or 60%, which corresponds, respectively, to an
abbreviation M40, M50 and M60.
wo 2016/012718 14 PCT /FR20 15/052016
P means tert-butyl peroxybenzoate (peroxide) and is conventionally
sold in pure form. It is sold by the Applicant under the name Luperox® P.
101 means 2,5-dimethyl 2,5-di(tert-butylperoxy)hexane and is
conventionally sold in pure or virtually pure form. This peroxide is sold by the
5 Applicant under the name Luperox® 101.
270 means tert-butyl peroxy-3,5,5-trimethylhexanoate and is
conventionally sold in pure or virtually pure form. This peroxide is sold by the
Applicant under the name Luperox® 270.
531 M80 means 1, 1-bis(tert-amylperoxy)cyclohexane diluted to
10 80% in isododecane, for example. This peroxide is sold by the Applicant under
the name Luperox® 531 M80.
15
331 M50 means 1, 1-bis(tert-butylperoxy)cyclohexane diluted to
50% in isododecane, for example. This peroxide is sold by the Applicant under
the name Luperox® 331M50.
JWEB50 means poly(t-butyl) peroxycarbonate polyether diluted to
50% in ethyl benzene, for example. This peroxide is sold by the Applicant under
the name Luperox® JWEB50.
EVA means an ethylene-vinyl acetate copolymer. The same type of
EVA is used for all the experiments and tests in order to ensure that the results
20 are not dependent on the type of EVA used. By way of example, as mentioned
previously, mention will be made of Evatane® 18-150 sold by the Applicant and
which consists of an EVA with 18% vinyl acetate and 150 as melt flow index
(MFI) value measured according to standard ASTM 1238 or Evatane® 40-55
sold by the Applicant and which consists of an EVA with 40% vinyl acetate and
25 55 as melt flow index (MFI) value measured according to standard ASTM 1238.
Tests performed and results:
In all the figures, the term "phr" means "per hundred resin". Thus,
by way of example, if 1 phr is considered for a given peroxide, this means that,
30 in the composition tested, there is 1 unit (by weight) of this peroxide present per
100 units of the polymer to be crosslinked.
wo 2016/012718 15 P(T /FR20 15/052016
Figure 1 shows the crosslinking density measurements for an EVA
with a peroxide.
TBEC is considered as the reference for a crosslinking at
3.38 dN.m for 1 phr. It is observed that, with respect to this peroxide TBEC
5 conventionally used for crosslinking EVA, the other standard peroxides P, 101,
270, 531M80, 331M50 and JWEB50 must be present in larger or even very
(very) much larger amounts to obtain the same level of crosslinking as TBEC.
Only TBIC, to obtain the same level of crosslinking, requires a
smaller amount, i.e. in the present case 0.9 phr. Thus, the use of TBIC makes it
I 0 possible to reduce the costs (due to the smaller amount) and thus the level of
volatile organic compounds originating from the decomposition of the peroxide
itself in the crosslinked EVA.
Figure 2 makes it possible to draw two main conclusions. Firstly,
15 the TBIC used in very small amount (0.2 phr) makes it possible to drastically
increase the volume resistivity of the crosslinked polymer and that TBIC alone
has much better results than TBEC alone. Finally, it will also be noted that a
virtually equivalent (50/50) mixture of TBIC and TBEC has a synergistic effect
since the results observed on this VR test are the best.
20
Figure 3 confirms the conclusion that the TBIC + TBEC mixture, in
specific respective proportions, has the best results on the VR test.
Figure 4 makes it possible in particular to establish that the diluent
25 or solvent, in the present case isododecane, has no impact on the volume
resistivity measurement.
30
It will be noted here that the solvent used for TBIC is isododecane,
but that other organic solvents were tested and that the results are identical or
virtually identical to those presented here.
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wo 2016/012718 16 PCT /FR20 15/052016
Figure 5 makes it possible mainly to establish the fact that TBIC
achieves rapid crosslinking of the polymer and that the shorter the crosslinking
time, the higher the level of volume resistivity, which allows precise metering of
the desired level of volume resistivity for the polymer to be crosslinked.
5 It will be noted here that, although all the tests presented in the
context of this patent application were performed with EVA, many other
polymers usually crosslinked were tested as a mixture with EVA (in a fraction of
the latter that is occasionally low or even very low), or even without EVA
(replaced with another polymer), and all have identical or virtually identical
10 results and conclusions (as regards TBIC).
Figure 6 shows again that small amounts of TBIC make it possible
to obtain the best results on the VR test.
It is clearly understood here that the amount of TBIC defined as
15 preferred ranges, or even more preferred ranges, is admittedly dependent on
this result on the VR test, but also on other parameters such as, in particular,
the thermomechanical properties of the crosslinked polymer.
wo 2016/012718 17 l'CT /FR20 15/0520 16

CLAIMS
1. Use of peroxide(s) for crosslinking at least one polymer, the
said polymer consisting of an ethylene homopolymer or copolymer and in
5 particular the ethylene-vinyl acetate (EVA) copolymer or a mixture of EVA with
another ethylene homopolymer or copolymer, characterized in that the peroxide
comprises 0,0-tert-butyl 0-isopropyl monoperoxycarbonate or 0,0-tert-amyl
0-isopropyl monoperoxycarbonate (TA-IPC) as well as 0,0-tert-butyl 0-2-
ethylhexyl monoperoxycarbonate or 0,0-tert-amyl 0-2-ethylhexyl
I 0 monoperoxycarbonate.
2. Use according to Claim 1, characterized in that the
peroxide consists of a mixture of 0,0-tert-butyl 0-isopropyl
monoperoxycarbonate and of 0,0-tert-butyl 0-2-ethylhexyl
15 monoperoxycarbonate or of 0,0-tert-amyl 0-2-ethylhexyl
monoperoxycarbonate, or 0,0-tert-amyl 0-isopropyl monoperoxycarbonate
and 0,0-tert-butyl 0-2-ethylhexyl monoperoxycarbonate or 0,0-tert-amyl 0-2-
ethylhexyl monoperoxycarbonate, preferably in a mass ratio of 99%/1% to
1%/99% of these two peroxides forming the said mixture, more preferentially
20 from 40%/60% to 60%/40% of these two peroxides forming the said mixture,
and even more preferentially in a mass ratio of from 45%/55% to 55%/45% of
these two peroxides forming the said mixture.
3. Use according to Claim 1 or 2, characterized in that 0,0-
25 tert-butyl 0-isopropyl monoperoxycarbonate or 0,0-tert-amyl 0-isopropyl
monoperoxycarbonate is in dilute form, preferably present in an amount of
greater than 50% in the dilution, and even more preferably present in an
amount of greater than 60% in the dilution.
30 4. Crosslinkable composition comprising at least one
ethylene-vinyl acetate (EVA) copolymer and at least one peroxide,
5
wo 2016/012718 18 PCT /FR20 15/052016
characterized in that the peroxide comprises 0,0-tert-butyl 0-isopropyl
monoperoxycarbonate or 0,0-tert-amyl 0-isopropyl monoperoxycarbonate as
well as 0,0-tert-butyl 0-2-ethylhexyl monoperoxycarbonate or 0,0-tert-amyl
0-2-ethylhexyl monoperxoycarbonate.
5. Crosslinkable composition according to Claim 4,
characterized in that the peroxide consists of a mixture of 0,0-tert-butyl 0-
isopropyl monoperoxycarbonate or of 0,0-tert-amyl 0-isopropyl
monoperoxycarbonate and of 0,0-tert-butyl 0-2-ethylhexyl
10 monoperoxycarbonate or of 0,0-tert-amyl 0-2-ethylhexyl
15
monoperoxycarbonate (TAEC}, preferably in a mass ratio of from 40% to 60%
of these two peroxides forming the said mixture, more preferentially in a mass
ratio of 45% to 55% of these two peroxides forming the said mixture.
6. Crosslinkable composition according to Claim 5,
characterized in that the peroxide mixture represents between 0.2% and 4%
and preferably between 0.5% and 2.5% of the mass amount of the polymer
present in the said composition.
20 7. Crosslinkable composition according to any one of Claims
4 to 6, characterized in that the said ethylene-vinyl acetate (EVA) copolymer is
present in the said composition in a content ranging from 70% to 99.9% and
preferably from 97% to 99% by weight relative to the weight of the composition.
25 8. Crosslinkable composition according to Claim 4,
characterized in that it also comprises one or more crosslinking coagents or
promoters.
9. Crosslinkable composition according to the preceding
30 claim, characterized in that the said functional agent is present in the said
composition in a content ranging from 0.05% to 30% by weight and
wo 2016/012718 19 PCT /FR20 15/052016
preferentially from 0.1% to 10% by weight relative to the weight of the
composition.
10. Process for manufacturing a film of crosslinked polymer,
5 characterized in that it comprises at least the following steps:
- a0
) extrusion in the form-of a film of a crosslinkable composition
according to any one of Claims4 to 9,
- bo) crosslinking of the said crosslinkable composition after the
said extrusion step ao) for a time of not more than twenty minutes, preferably
10 less than fifteen minutes.