FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“USE OF A FLUID POLYMERIC COMPOSITION
FOR ENCAPSULATING PHOTOVOLTAIC
MODULES”
ARKEMA FRANCE of 420, Rue d'Estienne d'Orves,
F-92700 Colombes, France.
The following specification particularly describes the invention and the
manner in which it is to be performed.
2
TECHNICAL FIELD OF THE INVENTION
The invention falls within the field of the
fabrication of photovoltaic modules. More particularly, it
relates to the use of a fluid polymeric composition for
encapsulating photovoltaic modules.
PRIOR ART
Photovoltaics is an energy-producing technology in
full expansion, which has the advantage of not emitting
greenhouse gases unlike fossil fuels, and of which the
fuel, which is light, is inexhaustible. In addition to
being ecological, photovoltaics is practical since a
photovoltaic module makes it possible to supply with
electricity an isolated dwelling or devices which cannot be
connected to the electrical circuit, such as cell phones,
ticket machines, bus shelters, etc.
A photovoltaic module, or solar panel, is an
electrical generator which makes it possible to convert
solar energy into a direct current. It generally consists
of an assembly of photovoltaic cells based on a
semiconductor material such as silicon, which are connected
to one another electrically in series and/or in parallel.
It is known practice to encapsulate this assembly of
photovoltaic cells in a material usually denoted by the
term “encapsulant”. The encapsulant generally comprises an
upper part and a lower part, the photovoltaic cells being
blocked between these two parts. To complete the
photovoltaic module, a protective front sheet and a
protective backsheet are placed against each face of the
encapsulant. The role of the encapsulant consists in
3
keeping the cells linked, in electrically insulating them
and in protecting them against the exterior environment, in
particular water and air.
The encapsulant is generally based on ethylene/vinyl
acetate (EVA) copolymer as has been described in patent
application JP 19870174967, which constitutes the technical
solution that is currently the most widely used. The
polymeric composition used as encapsulant is in the form of
a film with a thickness of typically between 50 μm and
20 mm. The film may be a monolayer or multilayer.
In a conventional process for fabricating a
photovoltaic module, several steps are required for the
encapsulation of the cells.
In a very first step, the polymeric composition used
as encapsulant is prepared by copolymerization, typically
by radical copolymerization.
This polymeric composition is then mixed with
additives using known techniques for mixing thermoplastic
materials, such as extrusion or blending. The conventional
additives added to the polymeric composition are thermally
activated peroxides for crosslinking the polymeric
composition, silanes for improving the adhesive properties
and anti-UV agents for improving the UV resistance.
The mixture obtained is then formed in the form of a
film using known techniques such as pressing, blown film
extrusion, extrusion-lamination, extrusion-coating, cast
film extrusion and calendering.
The photovoltaic cells are then encapsulated in the
polymer film. Typically, the following are successively put
together: a protective backsheet, a first layer of
encapsulating polymer film, the photovoltaic cells, a
second layer of encapsulating polymer film and then,
finally, a protective front sheet. The layers are assembled
by pressing techniques combined with heat treatment, such
4
as hot pressing, vacuum pressing and hot lamination. When
the temperature reaches the melting point of the polymeric
composition, the latter flows all around the assembly of
photovoltaic cells. Then, when the temperature reaches the
activation temperature of the crosslinking agent (typically
around 150°C), the polymeric composition crosslinks,
thereby making it possible to obtain a very strongly and
irreversibly bonded, compact assembly.
The fabrication of photovoltaic modules using films of
polymeric composition is, for example, described in
International patent application WO 2010/067040. Other
elements regarding the fabrication of photovoltaic modules
can be found, for example, in the publication “Handbook of
Photovoltaic Science and Engineering”, Wiley, 2003.
This process for fabricating photovoltaic modules,
which currently constitutes the most widely used
fabrication process, makes it possible to obtain
photovoltaic modules with satisfactory properties: good
adhesion of the various layers, little delamination of the
various layers, resistance to abrasion and to impacts,
impermeability to water and to atmospheric oxygen, etc.
However, this process has the major drawback of requiring
at least four successive steps (copolymerization, mixing
with additives, forming in the form of a film and pressing
with heat treatment). Each of these steps requires a
specific material. The complete preparation process is
therefore lengthy and expensive. In addition, the final
pressing step with heat treatment is a treatment step which
can only be carried out in batches (batch process). Those
skilled in the art do not at the moment have available a
method which enables the continuous fabrication of
photovoltaic modules.
There is therefore currently a need to provide a
process for the fabrication of photovoltaic modules which
5
is shorter, which comprises fewer steps, which is faster to
carry out and which is less expensive. Furthermore, there
is also the need to provide a continuous process for the
fabrication of photovoltaic modules.
SUMMARY OF THE INVENTION
A subject of the invention is the use, as encapsulant
in a photovoltaic module, of a polymeric composition, said
polymeric composition comprising a copolymer which
comprises an ethylene monomer and a carboxylic acid vinyl
ester comonomer, the carboxylic acid vinyl ester comonomer
representing between 5% and 50% by weight, relative to the
total weight of the copolymer, and the polymeric
composition having a Brookfield viscosity, measured at
120°C, of between 10 000 mPa.s and 25 000 mPa.s.
DETAILED DESCRIPTION
It is specified that, throughout this description, the
expression “between” should be understood to include the
limits mentioned.
The polymeric composition used according to the
invention comprises a copolymer. Said copolymer comprises
at least one ethylene monomer and at least one carboxylic
acid vinyl ester comonomer. The copolymer may optionally
comprise other comonomer(s).
Preferably, the carboxylic acid vinyl ester comonomer
can be chosen from the group consisting of vinyl acetate,
vinyl 2-ethylhexanoate (V2EH), vinyl octanoate and versatic
acid vinyl ester. Among these comonomers, vinyl acetate is
preferred. The copolymer is therefore, in this case, an
ethylene/vinyl acetate copolymer.
The copolymer comprises from 5% to 50%, preferentially
from 10% to 40%, more preferentially from 15% to 35% by
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weight of carboxylic acid vinyl ester comonomer, relative
to the total weight of the copolymer.
Moreover, the copolymer may comprise from 50% to 95%,
preferentially from 60% to 90%, more preferentially from
65% to 85% by weight of ethylene monomer, relative to the
total weight of the copolymer.
The amounts of the various comonomers present in the
copolymer can be measured by infrared spectroscopy using
ISO standard 8985 (1998).
Preferentially, the copolymer consists of an ethylene
monomer and of a carboxylic acid vinyl ester comonomer.
However, it is also possible for the copolymer to comprise
one or more other comonomers which can be chosen from alkyl
and hydroxyalkyl acrylates and methacrylates, such as
methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, butyl acrylate, butyl methacrylate,
hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-
ethylhexyl acrylate, 2-ethylhexyl methacrylate, propyl
acrylate, propyl methacrylate, isopropyl acrylate,
isopropyl methacrylate, n-butyl acrylate, n-butyl
methacrylate, isobutyl acrylate, isobutyl methacrylate,
tert-butyl acrylate, tert-butyl methacrylate, n-pentyl
acrylate, n-pentyl methacrylate, neopentyl acrylate,
neopentyl methacrylate, hexyl acrylate, hexyl methacrylate,
heptyl acrylate, heptyl methacrylate, octyl acrylate, octyl
methacrylate, neooctyl acrylate, neooctyl methacrylate,
nonyl acrylate, nonyl methacrylate, neononyl acrylate,
neononyl methacrylate, decyl acrylate, decyl methacrylate,
neodecyl acrylate, neodecyl methacrylate, lauryl acrylate,
lauryl methacrylate, palmityl acrylate, palmityl
methacrylate, stearyl acrylate or stearyl methacrylate. The
total weight of one or more other comonomers, relative to
the total weight of the copolymer, may be between 0% and
7
20%, preferentially between 5% and 15%, more preferentially
between 5% and 10%.
The copolymer according to the invention can be
obtained by polymerization according to the process
indicated hereinafter:
The copolymer can be prepared by means of a highpressure
radical polymerization process. The polymerization
can be carried out, for example, in a stirred or tubular
autoclave reactor. The pressure inside the reactor may be
between 1000 bar and 3000 bar, preferentially between
1500 bar and 2500 bar. The temperature during the
initiation of the reaction may be between 100°C and 300°C,
advantageously between 100°C and 170°C. The maximum
reaction temperature may be between 180°C and 300°C and
preferably between 200°C and 280°C.
The copolymerization can be carried out by introducing
the ethylene monomer, the carboxylic acid vinyl ester
comonomer and an initiator for polymerization at high
pressure into an autoclave or tubular reactor at an initial
temperature. When a tubular reactor is used, the
introduction of the mixture of the ethylene monomer, the
carboxylic acid vinyl ester comonomer and the
polymerization initiator is preferably carried out at the
inlet of the tubular reactor, and optionally at at least
one other injection point located along the tubular
reactor. The term “multipoint injection technique” is then
used.
The amounts of the comonomers introduced are adjusted
according to the desired final content in the copolymer.
The amount of initiator can range between 10 ppm and
1000 ppm by weight, preferentially between 10 ppm and
800 ppm, more preferentially between 10 ppm and 500 ppm,
relative to the monomers introduced.
8
All the organic and inorganic compounds which release
free radicals under the reaction conditions can be used as
polymerization initiator. Preferably, a compound or
mixtures of compounds comprising at least one peroxide
group can be used. The polymerization initiator can
preferentially be chosen from the group consisting of
peroxy esters, diacyls, percarbonates, peroxy ketals,
dialkyls, hydroperoxides, and mixtures thereof.
Advantageously, the polymerization initiator can be chosen
from the group consisting of tert-butyl peroxy esters, the
ester group of which contains from 5 to 10 carbon atoms,
such as tert-butyl peroxyneodecanoate, tert-butyl peroxy-2-
ethyl hexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate
and tert-butyl peroxypivalate, or it may be di-tert-butyl
peroxide. These peroxides are particularly suitable for the
copolymerization reaction described herein.
In addition to the monomers and to the initiator, use
may advantageously be made of a transfer agent in
proportions, relative to the total amount of monomers by
weight, of between 0% and 4%, preferentially of between
0.1% and 3%, more preferentially of between 0.3% and 0.6%.
These transfer agents make it possible to control the
molecular weights of the copolymer formed. The transfer
agent can be chosen from aliphatic ketones or aldehydes. It
is preferably chosen from propanaldehyde and MEK (methyl
ethyl ketone).
Generally, the amounts of initiator and of transfer
agent are adjusted so as to obtain a copolymer having the
desired Brookfield viscosity of from 10 000 to 25 000 mPa.s
at 120°C, which can correspond to a number-average
molecular weight (Mn) of between 6000 and 12 000 and to a
weight-average molecular weight (Mw) of between
20 000 g/mol and 60 000 g/mol.
9
At the end of the copolymerization, a residual amount
of less than 700 ppm of the transfer agent may be contained
in the final copolymer. The initiator is, for its part,
totally decomposed.
The polymeric composition used according to the
invention comprises the copolymer as described above. The
copolymer may represent between 92% and 99.9%,
preferentially between 97.5% and 99.5%, relative to the
total weight of the polymeric composition. In addition, the
polymeric composition may comprise other compounds, which
are generally denoted by the term “additives”. These
additives may represent, in total, between 0.1% and 10%,
preferentially between 0.5% and 3.5%, relative to the total
weight of the polymeric composition.
The additive(s) which may be included in the polymeric
composition can be chosen from those known to those skilled
in the art as additives present in the polymeric
compositions in the form of a film serving as encapsulant.
Quite particularly, the polymeric composition
according to the invention may comprise a crosslinking
agent. The function of the crosslinking agent is to
crosslink the copolymer present in the polymeric
composition after deposition thereof on the photovoltaic
cells. The crosslinking makes it possible to improve the
thermomechanical properties of the encapsulant, in
particular at high temperature. The crosslinking agent can
be chosen from thermally activated crosslinking agents,
irradiation-activated crosslinking agents, or the like.
Preferably, the crosslinking agent is a thermally activated
crosslinking agent, preferentially a peroxide.
Advantageously, the crosslinking agent is chosen from the
group consisting of O,O-tert-butyl O-(2-ethylhexyl)
monoperoxycarbonate, O-(2-ethylhexyl) O,O-tert-pentyl
peroxycarbonate, tert-butyl hydroperoxide, 2,5-dimethyl10
2,5-di(tert-butylperoxy)hexane, tert-butyl 2-ethylperoxyhexanoate
and 1-1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane.
The crosslinking agent can represent, in total,
between 0.1% and 5%, preferentially between 0.5% and 2.5%,
more preferentially between 0.7% and 2% by weight, relative
to the total weight of the polymeric composition.
Moreover, the polymeric composition according to the
invention may comprise a co-crosslinking agent. The cocrosslinking
agents advantageously make it possible to
accelerate the rate of crosslinking and/or to optimize the
degree of crosslinking achieved. The co-crosslinking agent
can in particular be chosen from multifunctional monomers
bearing at least 2 vinyl functions. Mention may be made,
for example, of triallyl isocyanurate or triallyl cyanate.
In addition, the polymeric composition according to
the invention may comprise a coupling agent. The coupling
agents advantageously make it possible to improve the
adhesion between the polymeric composition and the other
elements of the photovoltaic module. The coupling agent may
in particular be chosen from organic titanates or silanes.
Advantageously, the coupling agent is chosen from the group
consisting of silanes, for example 3-trimethoxysilylpropyl
methacrylate or vinyltrimethoxysilane.
Furthermore, the polymeric composition according to
the invention may comprise a UV-absorbing agent. These
agents are known to extend the lifetime of the photovoltaic
module by preventing the damage to the various components
caused by UV radiation. The UV-absorbing agent may in
particular be chosen from benzotriazoles or benzophenones.
The polymeric composition according to the invention
may also comprise a hindered amine light stabilizer (HALS)
and/or an antioxidant. The role of these additives is also
to extend the lifetime of the photovoltaic module. By
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virtue of their antioxidant properties, they protect the
various constituents of the module against the damaging
effects of the radicals which can be created by exposure to
UV radiation or to heat. The HALS may in particular be
chosen from bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate,
poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-
2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-
hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] or
else bis(1,2,2,6,6-pentamethyl-4-piperidyl) [[3,5-bis(1,1-
dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate. The
antioxidant may in particular be chosen from
pentaerythrityl tetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)
propionate, octadecyl 3-(3,5-di-tert-butyl-4-
hydroxyphenyl)propionate or tris(2,4-di-tert-butylphenyl)
phosphite.
The addition of these various additives can be carried
out by methods known to those skilled in the art, such as
the use of a melting pot or of an internal mixer or by
impregnation in the case of additives in liquid form.
The polymeric composition which is used according to
the invention has a Brookfield viscosity, measured at
120°C, of between 10 000 mPa.s and 25 000 mPa.s, and
preferentially between 12 000 mPa.s and 23 000 mPa.s.
The viscosity measurements were carried out on a
Brookfield viscometer. The reference temperature is taken
at 120°C. The measurements can in particular be carried out
according to the following procedure:
The equipment used is a Brookfield RV-DVIII rheometer.
A spindle of cylindrical geometry with conical ends (type
SC4-27 or SC4-29 depending on the viscosity range studied)
is immersed in the sample, the temperature of which is
regulated at 120°C. The spindle is rotated at a speed of
20 revolutions per minute. The resistance applied by the
sample against the rotation of the spindle is measured and
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makes it possible to calculate the viscosity of said
sample.
By virtue of its particular physicochemical
properties, the polymeric composition according to the
invention can be used as an encapsulant in a photovoltaic
module in an entirely novel manner.
Indeed, by virtue of its relatively low viscosity, the
polymeric composition can be cast and can be applied
directly to the assembly of photovoltaic cells. It is
therefore no longer necessary to form the polymeric
composition serving as encapsulant in the form of a film
before using it.
The present invention therefore also relates to a
process for the fabrication of a photovoltaic module,
wherein one or more photovoltaic cells are encapsulated
with the polymeric composition described above. A subject
of the invention is also a particular process for
encapsulating a photovoltaic module, comprising the steps
consisting in:
a) obtaining a polymeric composition comprising:
- a copolymer comprising an ethylene monomer and
a carboxylic acid vinyl ester comonomer, the
carboxylic acid vinyl ester comonomer representing
between 5% and 50% by weight, relative to the total
weight of the copolymer, and
- a crosslinking agent,
the polymeric composition having a Brookfield viscosity,
measured at 120°C, of between 10 000 mPa.s and
25 000 mPa.s;
b) forming a stack comprising, in order, a protective
backsheet, a first layer of the polymeric composition, an
assembly of photovoltaic cells, a second layer of the
polymeric composition, and a protective front sheet; then
13
c) applying an activation treatment suitable for the
crosslinking agent in order to crosslink the composition.
The step consisting in obtaining the polymeric
composition may comprise the steps consisting in
synthesizing the suitable copolymer or in procuring it
directly in final form, then in mixing it with a
crosslinking agent and optionally with other additives.
These various steps, and also the compositions used, may be
as described above in the present text. Alternatively, it
is also possible to procure the polymeric composition
comprising the copolymer and the thermally activated
crosslinking agent in already mixed form.
During the stack formation step, the layers of the
polymeric composition according to the invention can be
deposited by any means known to those skilled in the art
without prior forming. The relatively low viscosity of the
polymeric composition in the molten state makes it possible
to use techniques known in particular in the paint field,
for example by means of a roll, or in the hot-melt field,
for example by coating with a bar-coater.
Once the stack has been formed, an activation
treatment suitable for the activation agent is carried out,
so as to crosslink the polymeric composition. For example,
in the case of a thermally activated crosslinking agent,
this step may consist in thermally treating the stack at a
temperature above the activation temperature of the agent
for crosslinking the polymeric composition.
Polymeric compositions comprising an ethylene/vinyl
acetate copolymer and having a Brookfield viscosity
sufficiently low to be flowable are already currently known
under the name Evazole® sold by the company Arkema. These
compositions are conventionally used as an additive in
fuels.
14
However, the inventors have discovered that, the lower
the viscosity of the polymeric composition, the more
difficult it becomes to satisfactorily crosslink the
copolymer, until a critical viscosity is reached below
which the polymeric composition is no longer crosslinkable.
Thus, the Evazole® product range is not applicable for a
photovoltaic encapsulant application.
It is therefore entirely surprising that the polymeric
composition described in the present invention has both a
viscosity such that the composition can be directly applied
as a paint, and good crosslinkability.
The photovoltaic modules obtained by means of the
process as described above have properties which are at
least as satisfactory as the modules obtained by means of a
conventional encapsulation process using an encapsulant
film. In particular, it has been noted that the various
layers of the modules obtained according to the process of
the present invention have good adhesion between them and
that the modules show no delamination problems.
The process which is the subject of the present
invention can be advantageously be carried out
continuously. Indeed, the stack formation and heat
treatment steps can be carried out continuously according
to conventional methods.
Other objectives, characteristics and advantages of
the invention will emerge from the following exemplary
embodiments, which are given purely by way of illustration
and are in no way limiting, and which refer to the appended
figure 1 which is a graph representing the curves of change
in elastic modulus G’ (in Pa) of the exemplified
compositions as a function of time t (in s).
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EXAMPLES
1) Synthesis of the copolymer/characterization of the
Brookfield viscosity:
In examples 1 and 2, two copolymers were synthesized
from the following reagents:
Test
Vinyl acetate
(% by weight)
Transfer agent
injected
(% by weight)
Peroxide
content
(ppm by weight)
Example 1 28 0.5 162
Example 2 28 0.4 186
Another copolymer was prepared under conditions making
it possible to obtain a Brookfield viscosity of less than
10 000 mPa.s. This is counter example 1.
Test
Vinyl acetate
(% by weight)
Transfer agent
injected
(% by weight)
Peroxide
content
(ppm by weight)
Counter
example 1
28 2 244
Finally, counter example 2 is a commercial grade
Evatane® 28800 supplied by the company Arkema, the
Brookfield viscosity of which is greater than 25 000 mPa.s.
The vinyl acetate comonomer content is 28% by weight.
These copolymers were characterized on a Brookfield
rheometer under the conditions described in the table
below:
16
Brookfield viscosity characterization conditions
Equipment Brookfield RV-DVIII rheometer
Spindle used SC4-27 or SC4-29
Characterization
temperature
120°C
Spindle rotation
speed
20 revolutions/minute
The Brookfield viscosities thus measured are given in
the table below:
Test
Spindle
used
Brookfield viscosity
at 120°C (mPa.s)
Example 1 SC4-29 13 450
Example 2 SC4-29 22 400
Counter example 1 SC4-27 525
Counter example 2 SC4-29 76 000
2) Preparation of the formulation/additivation:
The additivation of the copolymers with 3-trimethoxysilylpropyl
methacrylate (coupling agent) and with O,Otert-
butyl O-(2-ethylhexyl) monoperoxycarbonate
(crosslinking agent) was carried out by hot-mixing in a
melting pot regulated at 80°C and stirred at a speed of
250 rpm.
The additive contents are as described in the table
below:
17
Product
Content in the
formulation
(% by weight)
Ethylene/vinyl acetate copolymer 98.2
O,O-tert-butyl O-(2-ethylhexyl)
monoperoxycarbonate
1.5
3-Trimethoxysilylpropyl methacrylate 0.3
Total 100
3) Evaluation of crosslinkability:
The formulations obtained were then analyzed by
parallel-plate dynamic rheometry. The protocol followed is
as described in the table below:
Protocol for evaluating crosslinkability by parallelplate
rheometry
Rheometry Anton Paar – Model MCR 301
Plate diameter 50 mm
Gap 1 mm
Deformation amplitude 10%
Oscillation frequency 10 Hz
Procedure
time/temperature
80°C Initial
Ramp 80  150°C 14 minutes
Isotherm 150°C 30 minutes
Data obtained
Curve of change in elastic
modulus G’ (Pa) as a function
of time t (s)
Criterion representative
of the level of
crosslinking
Level of elastic modulus G’
after crosslinking greater than
or equal to 103 Pa at 150°C
18
The curves obtained for the various formulations are
given in figure 1.
On the basis of these curves, the levels of elastic
modulus G’ at 150°C after crosslinking were obtained. They
are given in the table below:
Test
Level of elastic modulus G’ at 150°C
after crosslinking (Pa)
Example 1 1450
Example 2 2000
Counter example 1 1.05
Counter example 2 65 800
4) Use of the encapsulant
The formulations were used by coating by means of a
bar-coater. The formulations were heated to a temperature
of 100°C and then cast on a glass substrate. The bar-coater
then made it possible to spread each formulation into a
layer of even thickness.
In the case of examples 1 and 2, and also of counter
example 1, the coating did not pose a problem and an even
layer could be obtained. However, given the excessively low
viscosity of counter example 1, the latter exhibits no
mechanical strength after cooling, even after the
crosslinking step. Examples 1 and 2, for their part,
exhibited good applicability, combined with good mechanical
strength after cooling. Finally, counter example 2, given
its relatively high viscosity, did not allow application by
means of this coating process.
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WE CLAIM:
1. The use, as encapsulant in a photovoltaic module, of a
polymeric composition, said polymeric composition
comprising a copolymer which comprises an ethylene monomer
and a carboxylic acid vinyl ester comonomer, the carboxylic
acid vinyl ester comonomer representing between 5% and 50%
by weight, relative to the total weight of the copolymer,
and the polymeric composition having a Brookfield
viscosity, measured at 120°C, of between 10 000 mPa.s and
25 000 mPa.s.
2. The use as claimed in claim 1, characterized in that
the carboxylic acid vinyl ester comonomer is chosen from
the group consisting of vinyl acetate, vinyl 2-
ethylhexanoate, vinyl octanoate and versatic acid vinyl
ester, and is preferentially vinyl acetate.
3. The use as claimed in either of claims 1 and 2,
characterized in that the copolymer comprises from 10% to
40%, more preferentially from 15% to 35% by weight of
carboxylic acid vinyl ester comonomer, relative to the
total weight of the copolymer.
4. The use as claimed in any one of claims 1 to 3,
characterized in that the copolymer consists of an ethylene
monomer and of a carboxylic acid vinyl ester comonomer.
5. The use as claimed in any one of claims 1 to 4,
characterized in that the copolymer represents between 92%
and 99.9%, preferentially between 97.5% and 99.5%, relative
to the total weight of the polymeric composition.
20
6. The use as claimed in any one of claims 1 to 5,
characterized in that the polymeric composition also
comprises a crosslinking agent, the crosslinking agent
representing in total between 0.1% and 5%, preferentially
between 0.5% and 2.5%, more preferentially between 0.7% and
2% by weight, relative to the total weight of the polymeric
composition.
7. The use as claimed in any one of claims 1 to 6,
characterized in that the polymeric composition has a
Brookfield viscosity, measured at 120°C, of between
12 000 mPa.s and 23 000 mPa.s.
8. A process for encapsulating a photovoltaic module,
comprising the steps consisting in:
a) obtaining a polymeric composition comprising:
- a copolymer comprising an ethylene monomer and
a carboxylic acid vinyl ester comonomer, the
carboxylic acid vinyl ester comonomer representing
between 5% and 50% by weight, relative to the total
weight of the copolymer, and
- a crosslinking agent,
the polymeric composition having a Brookfield viscosity,
measured at 120°C, of between 10 000 mPa.s and
25 000 mPa.s;
b) forming a stack comprising, in order, a protective
backsheet, a first layer of the polymeric composition, an
assembly of photovoltaic cells, a second layer of the
polymeric composition, and a protective front sheet; then
c) applying an activation treatment suitable for the
crosslinking agent in order to crosslink the composition.
9. The process as claimed in claim 8, characterized in
that the crosslinking agent is a thermally activated
21
crosslinking agent and step c) consists in heat treating
the stack at a temperature above the activation temperature
of the agent for crosslinking the polymeric composition.
10. The process as claimed in either of claims 8 and 9,
characterized in that it is carried out continuously.
Dated this 28th day of July, 2015
NAMRATA CHADHA
OF K&S PARTNERS
AGENT FOR THE APPLICANT(S)
22
ABSTRACT
Title: “USE OF A FLUID POLYMERIC COMPOSITION FOR ENCAPSULATING
PHOTOVOLTAIC MODULES”
The invention concerns the use of a polymeric composition as
an encapsulant in a photovoltaic module, said polymeric
composition comprising a copolymer that comprises an ethylene
monomer and a carboxylic acid vinyl ester comonomer, in
particular an ethylene vinyl acetate copolymer, and the
polymeric composition having a Brookfield viscosity measured
at 120°C of between 10,000 mPa.s and 25,000 mPa.s. The
invention further concerns a method for encapsulating a
photovoltaic module using this polymeric composition.