Multilayer polyamide film for rear panel of
photovoltaic module
FIELD OF THE INVENTION
The present invention relates to the use of a
multilayer film based on polyamides as rear protective
sheet in a photovoltaic module. It also relates to a
photovoltaic module including photovoltaic cells protected
10 by an encapsulant, a front protective sheet and a rear
protective sheet, in which the rear protective sheet
consists of a multilayer film based on polyamides.
BACKGROUND OF THE INVENTION
15
Global warming, related to the greenhouse gases given
off by fossil fuels, has led to the development of
alternative energy solutions which do not emit such gases
during the operation thereof, such as, for example,
20 photovoltalc modules. The latter can be used effectively to
supply electricity to a dwelling or to provide electricity
to devices which cannot be connected to the electrical
circult, such as cell phones, ticket machines, bus
shelters, and the like.
25
A photovoltaic module, or solar panel, is an
electrical generator r~rhich makes it possible to convert
solar energy into a direct current, composed of an assembly
of photovoltaic cells based on a semiconductor material,
30 such as silicon, which cells are connected to one another
electrically and are'protected by an adhesive encapsulating
material, generally based on ethylene/vinyl acetate (EVA)
copolymer or optionally based on a blend of polyethylene
and of a functionalized polyolefin (Dl0 2010/067040). An
upper protective sheet and a protective sheet at the back
of the module (or backsheet) are positioned against each
face of the encapsulant. Protection of the photovoltaic
5 cell from impact and moisture is provided by the front
protective sheet, generally made of glass or fluoropolymer,
while the role of the rear protective sheet is also to
protect the cell against moisture but also to ensure
electrical insulation of the cells, to block UV rays and to
10 present a good mechanical strength, in particular to
tearing. This rear protective sheet thus plays an essential
role in the longevity of the photovoltaic module.
The most effective solution currently consists in
15 using, as rear protective sheet, three-layered structures
including a central layer based on polyester, such as
polyethylene terephthalate (PET), providing electrical
insulation of the photovoltaic module and the mechanical
stability of the rear protective sheet, which is surrounded
20 by two layers based on fluoropolymer, such as
polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF) or
poly(ethylene/tetrafluoroethylene) (ETFE), which are
intended to protect the central layer against hydrolysis
and to provide the function of protection of the protective
25 sheet from UV radiation. This rear protective sheet
exhibits in particular a good dimensional stability at the
temperatures of rolling the photovoltaic module.
More recently, other materials for manufacturing the
30 rear protective sheet of photovoltaic modules have been
provided, such as polyolefins, in particular polyprop2lene
(650 2010/053936 and FO 2011/09568), which are optionally
grafted with polyamide (WO 2010/069546). These protective
sheets can additionally include a polyamide. However, their
performances are not optimal.
A suggestion has also been made to replace the PVDF
5 layers of the conventional structures with layers of
polyamide 12 (PA-12) which are presented as thinner and
less expensive (US 2010/119841 and US 2010/059105).
Structures of this type are sold in particular by
Isovoltaic under the commercial references lcosolara APA
10 3636 and APA 3552. As indicated above, the central PET
layer nevertheless has a tendency to hydroiyze and,
consequently, to depolymerize under certain moisture
conditions. This disadvantage has been overcome by the
structure sold by Isovoltaic under the reference lcosolara
15 AAA 3554, which includes a central PA-12 layer. Hornlever, it
has been demonstrated that this' type of structure,
comprising three PA-12 layers, exhibits a tendency to
relax/creep at the temperatures employed to manufacture the
photovoltaic module. This is because the process for the
20 manufacture of the module generally comprises a stage of
extrusion of the rear protective sheet and then of rolling,
at high temperature and under vacuum, the various sheets
forming the module, at a temperature sufficient to soften
the encapsulating material. It has been observed that, at
25 this temperature, the PA-12 in lcosolara AAA 3554 has a
tendency to retract. In order to overcome this
disadvantage, glass fibers have been added to the central
PA-12 layer in order to increase its viscosity and its heat
deflection temperature. The reinforcing of the central
30 layer has nevertheless rendered the rear protective sheet
more bkittle, which is not desirable. The document
US 2010/0324207 furthermore describes the use of a
monolayer structure based on Ce-C1? polyamide as rear
protective sheet. This structure presents the same problems
of retraction as that described above.
The document EP 2422976, which can be cited in
opposition solely under novelty, which in particular does
5 not disclose the characteristics of the CB layer of claim 1
of the patent application in question, is also known.
The present invention is targeted at overcoming the
disadvantages of the rear protective sheets of photovoltaic
modules by providing for the use, in their manufacture, of
10 a multilayer film based on two different types of polyamide
which exhibits all the properties required for this use, in
particular a low water uptake, sufficient electrical
insulation and efficient protection against UV radiation,
at an acceptable cost, in particular even lovrer than that
15 of the PAlZ/PA12/PA12 multilayer structures, without,
hovrever, exhibiting the problems of retraction observed
with the rear protective sheets including a central layer
based on PA-12.
20 SUMMARY OF THE INVENTION
A subject matter of the invention is thus the use of a
multilayer film as rear protective sheet in a photovoltaic
module comprising photovoltaic cells covered with an
25 encapsulant, characterized in that said film comprises:
- a CA layer including, as predominant polymer, at
least one polyamide A exhibiting a mean number of carbon
atoms per nitrogen atom of between 4 and 8,
- a CB layer including: (a) as predominant polymer, at
30 least one polyamide B exhibiting a mean number of carbon
atoms per nitrogen atom of between '8 and 15, the
polyamide(s) B exhibiting a mean number of carbon atoms per
nitrogen atom which is strictly greater than the mean
number of carbon atoms per nitrogen atom of the
polyamide(s) A, and (b) at least one additive for combating
UV radiation,
the CB layer being positioned between the encapsulant
5 and the CA layer.
Another subject matter of the invention is a
photovoltaic module including photovoltaic cells protected
by an encapsulant, a front protective sheet and a rear
10 protective sheet, in which the rear protective sheet
consists of a multilayer film comprising:
- a CA layer including, as predominant polymer, at
least one polyamide A exhibiting a mean number of carbon
atoms per nitrogen atom of between 4 and 8,
15 - a CB layer including: (a) as predominant polymer, at
least one polyamide B exhibiting a mean number of carbon
atoms per nitrogen atom of between 8 and 15, the
polyamide(s) B exhibiting a mean number of carbon atoms per
nitrogen atom which is strictly greater than the mean
20 number of carbon atoms per nitrogen atom of the
polyamide(s) A, and (b) at least one additive for combating
UV radiation,
the CB layer being positioned between the encapsulant
and the CA layer.
25
It is specified that, throughout this description, the
expression "of between" must be understood as including the
limits mentioned. In addition, by misuse of language, the
term "film" includes not only films proper, generally
30 having a thickness of less than 250 pm, and sheets, the
thickness of which is instead of between 250 and 1 mm.
DETAILED DESCRIPTION
5 According to the present patent application, the
term "polyamide", also denoted PA, is targeted at:
- homopolymers obtained by polycondensation of aliphatic
diamines and aliphatic diacids, or of a lactam or of an
a,y-aminocarboxylic acid,
10 - copolymers, or copolyamides, based on different amide
units, such as, for example, copolyamide 6/12 with amide
units derived from lactam-6 and lactam-12,
- polyamide compositions, such as polyamide alloys,
provided that the polyamide is the predominant
15 constituent thereof.
There also exists a category of copolyamides within a
broad sense which, aithough not preferred, comes within the
context of the invention. They are copolyamides comprising
20 nat only amide units (which are predominant) but also units
of nonamide nature, for example ether units. The best known
examples are PEBAs or polyether-block-amides, and their
copolyamide-ester-ether, copolyamide-ether or copolyamideester
variants. Mention may be made, among these, of PEBA-
25 12, where the polyamide units are the same as those of PA-
12, and PEBA-6.12, where the polyamide units are the same
as those of PA-6.12.
In this invention, the homopolyamides, copolyamides
30 and alloys having a given number of carbon atoms per
nitrogen atom are selected, it being known that there are
as many nitrogen atoms as amide (-CO-NH) groups.
In the case of a homopolyamide of PA-X.Y type, the
number of carbon atoms per nitrogen atom is the mean of the
X unit and of the Y unit. Thus, PA-6.12 is a PA comprising
9 carbon atoms per nitrogen atom, in other words is a Cs
5 PA. PA-6.13 is a Cg.5 PA. PA-12.T is a Clo PA, the T, that
is to say terephthalic acid, being a Cg group.
In the case of the copolyamides, the number of carbon
atoms per nitrogen atom is calculated according to the same
10 principle. The calculation is carried out on a molar pro
rata basis from the various amide units. Thus, 60/40mol%
coPA-6.T/6.6 is a C6.6 copolyamide: 60%(~6 +8)/ 2+40%x (6t6)/ 2
= 6.6. In the case of a copolyamide having units of
nonamide type, the calculation is carried out solely on the
15 portion of amide units. Thus, in the case of PEBA-12, which
is a block copolymer of amide-12 units and of ether units,
the carbon number will be 12; for PEBA-6.12, it will be 9.
In the case of the mixtures or alloys, the
20 calculation of the number of carbon atoms per nitrogen atom
is carried out solely on the fraction consisting of the
polyamides. For example, a composition with 67 parts by
weight of PA-12 (12 carbon atoms per nitrogen atom) and
33 parts by weight of PA-6 (6 carbon atoms per nitrogen
25 atom) will be a polyamide composition comprising 10 carbon
atoms per nitrogen atom, in other words a Clo composition.
The calculation is as follows: 12x67/(67+33) t
6x33/(67+33). In the case of a similar composition but
comprising, in addition, 40 parts of impact modifier EPR,
30 which is not a polyamide, the number of carbon atoms per
nitrogen atom will be equal to 10.
Homopolyamides are preferred for use as the
polyamide A.
The film used according to the invention includes a CA
5 layer comprising, as predominant polymer, at least one
polyamide A exhibiting a mean number of carbon atoms per
nitrogen atom of between 4 and 8. The term "predominant" is
understood to mean that the proportion by weight of the
polyamide A in the CA layer is greater than that of any
10 other polymer present in said layer. Generally, polyamide A
represents more than 30% by weight, for example more than
60% by weight, indeed even more than 90% by weight, with
respect to the weight of the CA layer, and the polyamide B
represents more than 50% by weight, for example more than
15 70% by weight, indeed even more than 90% by weight, with
respect to the weight of the CB layer.
~xim~leosf polyamides A are in particular PA-6, PA-8,
PA-6.6, PA-4.6, PA-6.10, copolyamide-6.T/6.6, copolyamide
20 6.1/6.6 and copolyamide 6.T/6.1/6.6, where I represents
isophthalic acid and T represents terephthalic acid, and
their blends. It is preferable to use PA-6. The melting
point of the polyamide A is preferably greater than or
equal to 210'~.
25
The film used according to the invention additionally
includes a CB layer including, as predominant polymer, at
least one polyamide B exhibiting a mean number of carbon
atoms per nitrogen atom of between 8 and 15, the
30 polyamide(s) B exhibiting a mean number of carbon atoms per
nitrogen atom strictly greater than the mean number of
carbon atoms per nitrogen atom of the polyamide(s).
Examples of polyamide B are in particular PA-8, PA-9,
PA-11, PA-12, PA-6.10, PA-10.10, PA-10.12, PA-6.12,
PA-6.14, PA-6.18, copolyamide 12/10.T, copolyamide ll/lO.T
or polyamide-12.T. It is preferable to use polyamides
5 having a mean number of 11 to 15 carbon atoms per nitrogen
atom, such as PA-12.
The polyamides A and B described above can be
obtained, in all or part, from resources resulting from
I0 renera~able starting materials, that is to say comprising
organic carbon of renewable origin determined according to
the standard ASTM D6866. It is the case in particular for
the sebacic acid used in PA-6.10 or the aminoundecanoic
acid which results in PA-11, both resulting from castor
15 oil.
The CB layer and optionally also the CA layer also
includes at least one additive for combating UV radiation.
The latter can be chosen in particular from opacifying
20 organic fillers, organic UV absorbers, UV stabilizers of
HALS type (that is to say, based on sterically hindered
amine) and their mixtures. Such additives are available in
particular from BASF under the ~inuvin' and ~vinul'
commercial references. The additive for combating UV
25 radiation can represent from 0.1% to 10% by weight,
preferably from 0.1% to 5% by weight, with respect to the
total weight of the CB or CA layer under consideration.
Inorganic fillers can also be used. They can be chosen from
titanium dioxide, zinc dioxide, zinc oxides or sulfides,
30 silica, quartz, alumina, calcium carbonate, talc, mica,
dolomite (CaC03-MgC03), montmorillonite (aluminosllicate) ,
barium sulfate (BaS04), ZrSi04, Fe=Od and their mixtures. In
this case, the filler or fillers for combating UV radiation
preferably represent from 0.1% to 50% by weight, preferably
from 5% to 30% by weight, with respect to the total weight
of the CB or CA layer under consideration.
5 Furthermore, at least one of the CA and CB layers
(preferably the CA layer) can be formulated so as to render
it adherent, respectively, to the CB layer or to the CA
layer (and/or to the encapsulant). In order to do this, it
is preferable for the CA layer to additionally include a
LO minor amount of polyamides A' and optionally A", vrhere:
(i) A' exhibits a mean number of carbon atoms per
nitrogen atom of between 7 and 10 and strictly greater than
that of A, and
(ii) A" exhibits a mean number of carbon atoms per
15 nitrogen atom of between 9 and 18 and strictly greater than
that of A'.
Likewise, the CB layer can include a minor amount of
polyamides B' and B", which respectively exhibit a mean
number of carbon atoms per nitrogen atom of between 4 and
20 8.5 and strictly less than that of B" and of between 7 and
10 and strictly less than that of B.
The difference in the mean number of carbon atoms per
nitrogen atom between A and A', between A' and A", between
B' and B' and between B" and B can be of between 1 and 4,
25 preferably between 2 and 3. The weighted mean of the
enthalpies of fusion of these polyamides within the CA or
CB composition is advantageously greater than 25 J/g
(measured by DSC) . Each of the polyamides A, A', A", B, B'
and B" can be a random, alternating or block polymer. They
30 are preferably aliphatic polymers. Examples of such
polyamides can be chosen from the lists indicated above.
It is thus preferable for the CA layer rendered
adherent to include the following proportions by weight of
A, A' and A":
A (such as PA-6) = 65-85%
A' (such as PA-6.12) = 3-8%
A" (such as PA-12) = 12-30%,
per 100% by weight of the A + A' t A" blend.
In an alternative form, it is possible to include at
10 least one tie layer in the multilayer film in order to
cause the CB layer to adhere to the CA layer and/or to the
encapsulant and/or to cause the CA layer to adhere to the
CB layer. Examples of suitable ties can be chosen from:
- one or more copolyamides comprising at least 25% by
15 weight of at least one monomer having a mean number of
carbon atoms per nitrogen atom of 4 to 6 and at least 25%
by weight of at least one comonomer having a mean number of
carbon atoms per nitrogen atom of 9 to 18 and their
mixtures, such as the following copolyamides: coPA-6/12
20 30/70%, coPA-6/12 50/50%, coPA-6/12 75/25%, coPA-6/6.10/12
25/50/25% and coPA-6/7/12 25/50/25%, and their blends, such
as the blend of coPA-6/12 80/20% and coPA-6/12 20/80%;
- one or more homopolyamides of PA-X.Y type, where X
ranges from 4 to 6 and Y ranges from 8 to 18, such as
25 PA-6,12, and their blends including at least 25% by weight
of diamine units for which X ranges from 4 to 6 and at
least 25% by weight of diacid units for which Y ranges from
8 to 18, such as the blends of PA-6.12 and PA-6.10, the
blends of PA-6.6 and PA-6.18 and the blends of PA-6.6,
30 PA-6.12 and PA-12.12;
- a blend of polyamides, sudh as described in
particular in the application EP 2 098 580, especially a
blend of PA-6, PA-6.12 and PA-i2;
- at least one functionalized polyolefin; and
- a blend of polyamide(s) and completely or partially
functionalized polyolefin(s) , such as the blends of PA-6,
PA-12 and functionalized polyolefin and the blends of
5 PA-6.12, PA-6 and functionalized polyolefin.
Examples of functionalized polyolefins comprise a
copolymer of at least one a-olefin, such as ethylene or
propylene, with at least one comonomer carrying a reactive
10 functional group chosen in particular from a carboxylic
acid, such as (meth)acrylic acid, a carboxylic anhydride,
such as maleic anhydride, or an epoxide, such as glycidyl
(meth)acrylate, and optionally at least one other comonomer
not carrying a reactive functional group chosen, for
15 example, from a different a-olefin; a diene, such as
butadiene; an unsaturated carboxylic acid ester, such as an
alkyl (meth)acrylate where the alkyl group can be a methyl,
ethyl or butyl group, in particular; and a carboxylic acid
vinyl ester, such as vinyl acetate.
It is preferable for the functionalized polyolefin to
include from 60% to 100% by weight of a-olefin and from 0%
to 40% by weight, preferably from 0% to 15% by weight, of
comonomer not carrying a reactive functional group. In
25 addition, it is preferable for the functionalized
polyolefin to include from 0.1% to 15% by weight,
preferably from 0.5% to 5% by weight, of comonomer carrying
a reactive functional group. Examples of such
functionalized polyolefins are the ethylene/acrylic
30 ester/glycidyl methacrylate and ethylene/acrylic
ester/maleic anhydride copolymers respectively available
from Arkema under the trade name ~otader" GMA and
LotaderO MAH, in particular Lotader0 AX 8840. Another
example of tie is the ethylene/alkyl acrylate/acrylic acid
terpolymer available from BASF under the trade name
~ucalen' A 3110 M. Mention may also be made of the
5 ethylene/vinyl acetate copolymers modified with maleic
anhydride available from Arkema under the Orevacm trade
name.
The composition of the CA and/or CB layers of the film
10 used according to the invention can additionally include
various additives, including inorganic or organic pigments,
dyes, optical brighteners, coupling agents, crosslinking
agents, plasticizers, such as butylbenzenesulfonamide
(BBSA), heat stabilizers, stabilizers with regard to
15 hydrolysis, antioxidants (for example of phenol and/or
phosphite and/or amine type), reinforcements, such as glass
fiber, flame retardants and their mixtures. On the other
hand, it is preferable for these layers not to include a
copper-based stabilizer.
The CA and/or CB layers advantageously additionally
include at least one impact modifier advantageously chosen
from functionalized polyolefins, for example polyolefins
functionalized by a carboxylic acid, such as (meth)acrylic
25 acid, a carboxylic anhydride, such as maleic anhydride, or
an epoxide, such as glycidyl (methlacrylate. Examples of
such impact modifiers comprise the functionalized
polyolefins described above as ties. The impact modifier
can represent from 2% to 40% by weight, with respect to the
30 total weight of the layer comprising it.
The film used according to the invention can have a
bilayer structure comprising only the CA and CB layers.
However, according to a preferred embodiment of the
invention, it can assume a structure comprising three
layers, consisting of a CA layer coated with a CB layer on
each of its faces. The thickness of each of the CA and CB
5 layers can, for example, be of between 15 pm and 500 pm,
for example between 20 and 350 pm, the multilayer film
having a total thickness of 200 to 1500 pm, for example
from 350 to 500 pm. In addition, it can comprise layers
other than the CA and CB layers and the optional tie
10 layers, such as layers forming a barrier to water, in
particular an aluminum sheet, or also one or more layers
based on a polyolefin, such as polypropylene or highdensity
polyethylene, optionally grafted with polyamide.
However, it is preferable for the film according to the
15 invention not to include a layer based on ethylene/vinyl
alcohol (EVOH) copolymer.
The film used according to the invention can be
manufactured according to conventional techniques for
20 producing films, sheets or plaques. Mention may be made, by
way of examples, of the techniques of blown film extrusion,
extrusion-lamination, extrusion-coating, cast film
extrusion or also extrusion of sheets. All these techniques
are known to a person skilled in the art and he will know
25 how to adjust the processing conditions of the various
techniques (temperature of the extruders, connector, dies,
rotational speed of the screws, cooling temperatures of the
cooling rolls, and the like) in order to form the structure
according to the invention having the desired shape and the
30 desired thicknesses. It would not be departing from the
invention if the final structure were obtained by pressing
or rolling techniques with adhesives in the solvent or
aqueous route or if the final structure were subjected to
an additional stage of annealing. The film used according
to the invention can additionally be provided in the sheet
or roll form.
5 The film according to the invention can be used as
rear protective sheet in a photovoltaic module. Such a
photovoltaic module can be manufactured according to the
processes known to a person skilled in the art and in
particular as described in US-5 593 532. In general, the
10 assembling of the various layers can be carried out by hot
or vacuum pressing, or hot rolling. The materials
constituting the upper protective sheet and the encapsulant
can also be chosen from those conventionally used in these
applications. Thus, the upper protective layer can comprise
15 glass, PMMA or a fluoropolymer and the encapsulant can
comprise at least one polymer, such as an ethylene/vinyl
acetate (EVA) copolymer, polyvinylbutyral (PVB), ionomers,
poly (methyl methacrylate) (PMMA) , a polyurethane, a
polyester, a silicone elastomer and their blends. The
20 photovoltaic cells can comprise monocrystalline or
polycrystalline doped silicon, amorphous silicon, cadmium
telluride, copper indium diselenide or organic materials,
for example.
25 The invention will now be illustrated by the following
nonlimiting example.
16
EXAMPLE
Preparation and evaluation of the properties of multilayer
films
Multilayer films having a thickness of between 350 and
450 pm are prepared by cast film extrusion on an extrusion
line of Dr Collin brand. This extrusion line is composed of
three extruders equipped with a standard polyolefin screw
10 profile, with a variable coextrusion block and with a
250 mm coathanger die. The coextrusion block allows the
production of a film of three layers (Layer l/Layer 2/Layer
3) with a variable distribution of thicknesses (e.g.:
25/300/25 pm). The parameters of the process are set thus:
15 - To extrusion layers 1 and 3: 220°C
- To extrusion layer 2: 220'~ or 240°C, according to the
polymers to be extruded
- To coextrusion box and die: 240"~
- line speed: 3 m/min
A comparative monolayer film of the same thickness was
in addition produced on the same line while feeding the
3 extruders with the same material. In this case, the
parameters of the process were set thus:
- To extrusion layers 1 and 3: 240°C
- To extrusion layer 2: 240'~
- To coextrusion box and die: 240°C
- line speed: 3 m/min
30 The compositions of the different layers are as
follows :
WO 2013/079861 PCTiFR20121052725
structure
-
Film 1
(according to
the
invention)
Fllm A
(comparative)
Film B
(comparative)
Film 2
(according to
the
invention)
Film C
(comparative)
Film 3
(according to
the
invention)
Film D
(comparative)
Film 4
(according to
the
invention)
* Measured after
expressed as percentage of increase in weight wlth respect to
the dry specimen conditioned overnight at 80°C under vacuum
Water
uptake
(%) *
5.8
1.8
9.1
6.7
1.35
3.4
7 . 0
4.8
17
Compositions of the
layers
PA12uv/PA6x/PA12uv
PA12uv/PA12uv/PA12uv
PA6uv
PA12uv/tie/PAG/tie/
PA12uv
PA12uv + Ti02/PA12uv
+ Ti02 + GF +
PP/PA12uv + Ti02
PA12uv + TiO,/PA6x +
TiO, + GF +
PP/PA12uv + TiOz
PA6uv + TiO2/PA6x +
Ti02 + GF + PP/PA6uv
+ Ti02
PA12uv + TiOz/PA6x +
TiO, + GF +
PP/PA12uv + Ti02
15 days on the film
Thicknesses of
the layers (pm)
25/300/25
25/300/25
350
25/25/250/25/25
25/300/25
25/300/25
25/300/25
25/300/25
steeped ln water and
where :
"PA12uv" denotes a PA-12 composition stabilized toward
UV radiation, including 99.15% of PA-12 with an MFI equal
to 20 (under 5 kg at 235"C), 0.2% of CIBA stabilizer
5 Tinuvin0 312, 0.15% of CIBA stabilizer lrgafosO 168 and
0.5% of CIBA stabilizer lrganoxa 245,
"PA6uv" denotes a PA-6 composition stabilized toward
UV radiation, including 99.15% of PA-6 with an MFI equal to
20 (under 2.16 kg at 235"C), 0.2% of CIBA stabilizer
10 Tinuvin" 312, 0.15% of CIBA stabilizer Irgafos" 168 and
0.5% of CIBA stabilizer ~rganox" 245,
"PA6x" denotes a PA-6 composition which has been
rendered adherent, including 69.15% of PA-6 with an MFI
equal to 20 (under 2.16 kg at 235'C), 5% of PA-6.12 with an
15 MFI equal to 10 (under 5 kg at 235OC), 15% of PA-12 r.rith an
MFI equal to 6 (under 5 kg at 235OC), 10% of copolymer of
ethylene, ethyl acrylate and maleic anhydride in a ratio by
weight 68.5/30/1.5 (NFI = 6 under 2.16 kg at 190°C), 0.2%
of CIBA stabilizer ~inuvin3~1 2, 0.15% of CIBA stabilizer
20 lrgafosO 168 and 0.5% of CIBA stabilizer lrganoxa 245,
"PA12uv + TiOzl' denotes a composition including 79.15%
of PA-12 with an MFI equal to 20 (under 5 kg at 235"~), 20%
of Ti02 of Tioxide' RTC30 type, 0.2% of CIBA stabilizer
~inuvin" 312, 0.15% of CIBA stabilizer lrgafosO 168 and
25 0.5% of CIBA stabilizer lrganoxa 245,
"PA12uv + TiO: + GF + PP" denotes a composition
including 54.15% of PA-12 with an MFI equal to 55 (under
5 kg at 235"C), 20% of TiO2of ~ioxide" RTC30 type, 10% of
Asahi glass fibers FT692, 15% of Mitsui polypropylene
30 grafted with maleic anhydride ~ d m e rQB~5 20E, 0.2% of CIBA
stabilizer Tinuvin0 312, 0.15% of' CIBA stabilizer lrgafosa
168 and 0.5% of CIBA stabilizer lrganoxa 245,
,,Tieu denotes a composition including 79.15% of PA-
6.12 with an MFI equal to 10 (under 5 kg at 235O~), 15% of
PA-6 xtrith, an MFI equal to 5 (under 5 kg at 235"C), 5% of
copolymer of ethylene, ethyl acrylate and maleic anhydride
5 in a ratio by weight 68.5/30/1.5 (MFI = 6 under 2.16 kg at
190°C), 0.2% of CIBA stabilizer ~inuvin' 312, 0.15% of CIBA
stabilizer 1rgafos0 168 and 0.5% of CIBA stabilizer
lrganoxa 245,
"PA6x + Ti02 + GF t PP" denotes a composition
10 including 34.15% of PA-6 with an MFI equal to 20 (under
2.16 kg at 235'C), 3% of PA-6.12 t~ith an MFI equal to 10
(under 5 kg at 235'C), 12% of PA-12 with an MFI equal to 6
(under 5 kg at 235"C), 5% of copolymer of ethylene, ethyl
acrylate and maleic anhydride in a ratio by weight
15 68.5/30/1.5 (MFI = 6 under 2.16 kg at 190°c), 20% of TiOz
of ~ioxide' RTC30 type, 10% of Asahi glass fibers FT692,
15% of Mitsui polypropylene grafted with maleic anhydride
~ d m e rQB~5 20E, 0.2% of CIBA stabilizer ~inuvin"3 12, 0.15%'
of CIBA stabilizer lrgafosa 168 and 0.5% of CIBA stabilizer
20 Irganoxe 245.
The abovementioned films are subject to an evaluation
of their thermomechanical stability, of their permeability
to water vapor and of their water uptake under conditions
25 corresponding to use in photovoltaic panels, according to
the following protocols.
Thernloillechanical stability
The thermomechanical strength of the various films is
30 evaluated by dynamic mechanical analysis. This test
consists in measuring the storage and loss moduli of the
material as a function of the temperature at a given
stressing frequency. For this, the DMA Q800 device from TA
is used. The measurements are carried out on the films in
tension at a stressing frequency of 1 Hz. The storage and
loss moduli are measured according to .a temperature
gradlent of 3"C/min ranging from -40°C to a temperature of
5 greater than 150°C which depends on a melting point of the
formulation. The thermomechanical strength at 150°C
(typical temperature for lamination of photovoltaic
modules) of the various formulations is evaluated through
the storage modulus at 1 Hz measured at this temperature.
10
Permeability to ~ 7 a t e rv apor
The permeability to water vapor (for "Moisture Vapor
Transmission Rate" or MVTR) is measured according to the
ASTM E96 E method (23'C/85% relative humidity).
15
Moisture uptake
The moisture content at saturation of the various
formulations is determined by conditioning the films at
20 85°C and 85% relative humidity, the temperature and
humidity conditions of the damp heat test used in the field
of photovoltaics. The moisture content is measured
according to the Karl-Fischer volumetric method with an
apparatus supplied by Metrohm. The desorption temperatures
25 are adjusted to the type of polyamide used in the
formulation (typically 170'~ for a PA-11/PA-12 and 200'~
for a PA-6) .
2 1

CLAIMS
1. The use of a multilayer film as rear protective
5 sheet in a photovoltaic module comprising photovoltaic
cells covered with an encapsulant, characterized in that
said film comprises:
- a CA layer including, as predominant polymer, at
least one polyamide A exhibiting a mean nunaer of carbon
10 atoms per nitrogen atom of between 4 and 8,
- a CB layer including: (a) as predominant polymer,
at least one polyamide B exhibiting a mean number of
carbon atoms per nitrogen atom of between 8 and 15, the
polyamide(s) B exhibiting a mean number of carbon atoms
15 per nitrogen atom which is strictly greater than themean
number of carbon atoms per nitrogen atom of the
polyamide(s) A, and (b) at least one additive for
combating UV radiation,
the CB layer being positioned between the
20 encapsulant and the CA layer.
2. The use as claimed in claim 1, characterized in
that the polyamide A is chosen from: PA-6, PA-8, PA-6.6,
PA-4.6, PA-6.10, copolyamide-6.T/6.6, copolyamide 6.1/6.6
25 and copolyamide 6.T/6.1/6.6, where I represents
isophthalic acid and T represents terephthalic acid, and
their blends, preferably PA-6.
3. The use as claimed in either of claims 1 and 2,
30 characterized in that the polyamide B is chosen from:
PA-8, PA-9, PA-11, PA-12, PA-6.10, PA-10.10, PA-10:12,
PA-6.12, PA-6.14, PA-6.18, copolyamide 12/10.T,
copolyamide 11/10.T or polyamide-12.T, the polyamides
preferably having a mean number of 11 to 15 carbon atoms
per nitrogen atom, such as PA-12.
4. The use as claimed in any one of claims 1 to
5 3, characterized in that the CA layer is rendered
adherent and in addition includes a minor amount of
polyamides A' and optionally A", where:
(i) A' exhibits a mean number of carbon atoms per
nitrogen atom of between 7 and 10 and strictly greater
10 than that of A, and
(ii) A" exhibits a mean number of carbon atoms per
nitrogen atom of betrareen 9 and 18 and strictly greater
than that of A'.
15 5. The use as claimed in any one of claims 1 to
4, characterized in that the CB layer includes a minor
amount of polyamides B' and B", which respectively
exhibit a mean number of carbon atoms per nitrogen atom
of between 4 and 8.5 and strictly less than that of B"
20 and of between 7 and 10 and strictly less than that of B.
6. The use as claimed in any one of claims 1 to
5, characterized in that the multilayer film additionally
comprises at least one tie layer in order to cause the CB
25 layer to adhere to the CA layer and/or to the encapsulant
and/or to cause the CA layer to adhere to the CB layer.
7. The use as claimed in claim 6, characterized in
that the tie is chosen from:
30 - one or more copolyamides comprising at least 25%
by weight of at least one monomer having a mean number of
carbon atoms per nitrogen atom of 4 to 6 and at least 25%
by weight of at least one comonomer having a mean number
of carbon atoms per nitrogen atom of 9 to 18, and their
blends;
- one or more homopolyamides of PA-X.Y type where X
ranges from 4 to 6 and Y ranges from 8 to 18, and their
5 blends including at least 25% by weight of diamine units
for which X ranges from 4 to 6 and at least 25% by weight
of diacid units for which Y ranges from 8 to 18;
- a blend of polyamides, in particular a blend of
PA-6, PA-6.12 and PA-12;
10 - at least one functionalized polyolefin; and
- a blend of polyamide(s) and completely or
partially functionalized polyolefin(s).
8. The use as claimed in any one of claims 1 to 7,
15 characterized in that the CA and/or CB layers
advantageously additionally include at least one impact
modifier chosen from functionalized polyolefins.
9. The use as claimed in either of claims 7 and 8,
20 characterized in that the functionalized polyolefin
comprises a copolymer of at least one a-olefin, such as
ethylene or propylene, with at least one comonomer
carrying a reactive functional group chosen in particular
from a carboxylic acid, such as (meth)acrylic acid, a
25 carboxylic anhydride, such as maleic anhydride, or an
epoxide, such as glycidyl (meth)acrylate, and optionally
at least one other comonomer not carrying a reactive
functional group chosen, for example, from a different aolefin;
a diene, such as butadiene; an unsaturated
30 carboxylic acid ester, such as an alkyl (methlacrylate
where the alkyl group can be a methyl, ethyl or butyl
group, in particular; and a carboxylic acid vinyl ester,
such as vinyl acetate.
. ~
. . ~. . ...
. .
10. The use as claimed in any one of claims. 1 to 9,~ . . . . ~.
characterized in.that the film hasa structure comprising
. ~
. .
. . three -layers consisting of .-a CA layer coated with a CB
5 iayer on each of its faces;
. . . . . .
.. . . . . . . .
. . . ~
11. A photovoltaic module including photovoltaic
. .
cells by an encapsulant', a: front protective
sheet and . a rear protective sheet, in which the rear
. . . . .
10 protective sheet . -consists of . a . multilayer : film
' - . comprising: . ~
. . . .
~ .~
- a CA layer .i nc.l.u ding, is. predominant polymer, at , ~ . . . .
least one polyamide Aexhibiting a mean number of carbon
. . .. . . ~.
atoms per nitrogen atom of be. tween 4 ~.a nd 8,
15 - a CB layer'including: (a). as predominant polymer,
at least one polyamide B exhibiting a mean number of
. .
carbon atoms per nitrogen atom of between 8 and' 15, the , .
polyamide (s) B exhibiting . a mean 'number of carbon. atoms
per nitrogen atom 1.111ichi s strictly greater than themean
. .
20 number of . carbon atoms .per nitrogen atom'. of the
polyamide(s) A, and (b) at least one additive for
- combating UV radiation, ,. .
the CB layer being positioned between the
encapsulant and the CA layer.