The present invention relates to a composition comprising a fluoropolymer and two white
inorganic fillers, the said composition being intended for the manufacture of thin
5 monolayer films, opaque to visible light and to UV radiation, which can be used in
particular in the field of photovoltaic cells.
It is essential, in a photovoltaic cell, to protect the constituent components against
environmental factors. Thus, the back part of the cell has to be protected by a polymer film
10 in order to prevent it from being damaged by ultraviolet (UV) rays and to prevent moisture
from penetrating. The protective film must have bulk or dimensional thermal stability in
order to avoid thermal expansion and in particular shrinkage during the assembling of the
cells. The photovoltaic cells are assembled by bonding the various layers using a solventbased
adhesive, followed by lamination. The use of solvents in adhesives may bring about
15 penetration of these solvents into the film. The cells are assembled at high temperature
(> 130°C) and optionally using a surface oxidation treatment of corona type. When the
protective film is based on fluoropolymer, this treatment can result in yellowing and in a
deterioration in the mechanical properties of the latter.
2 0 Furthermore, it is known to use fluoropolymers in general and in particular PVDF
(polyvinylidene difluoride) to manufacture films intended to protect objects and materials,
due to their very good resistance to bad weather, to UV radiation and to visible light, and
to chemicals. However, it is necessary for these films to exhibit a very good thermal
resistance for exterior applications subject to severe climatic conditions (rain, cold, heat) or
25 conversion processes carried out at high temperature (greater than 130°C). It is also
necessary for the films to exhibit good flexibility and good tensile strength, so as to
withstand the mechanical stresses during the positioning thereof on the object or the
material to be covered.
30 Generally, in order to protect a polymer film from damage by UV rays, UV absorbers
and/or inorganic fillers are incorporated therein. It is known that the addition of inorganic
fillers, such as Ti02, Si02, CaO, MgO, CaC03, AI2O3 and a great many others still, to a
fluoropolymer, such as a vinylidene fluoride polymer or copolymer (PVDF), can result in
fairly serious damage with production of hydrogen fluoride (HF) when the blending is
I
*
carried out in the molten state at high temperature in order to disperse the filler. One route
for processing these fillers with, for example, PVDF consists in introducing these inorganic
fillers using an acrylic masterbatch. To this end, the inorganic fillers are dispersed in a
methyl methacrylate polymer or copolymer (PMMA) and then this masterbatch is blended
5 with the PVDF in the molten state. The presence of a PMMA results in disadvantages,
such as a limitation on the dimensional stability of the film obtained with regard to
temperature, a lower thermal resistance, an odour characteristic of the acrylic during the
assembling of the cells and a lower stability to UV radiation in comparison with a pure
PVDF. Such a film comprising a tripartite fluoropolymer/acrylic polymer/inorganic filler
10 composition is described, for example, in the document WO 2009/101343. The proportion
of acrylic polymer varies from 5 to 45 parts per 100 parts of composition.
The Applicant Company has described, in Application FR 1 050 226, compositions based
on fluoropolymers and comprising just one inorganic filler which make it possible to
15 prepare films opaque to UV and visible radiation while retaining very good properties of
dimensional stability at the temperatures used for the manufacture of a backsheet and
subsequently of a photovoltaic panel. These compositions comprise a fluoropolymer and
zinc oxide (ZnO), the said filler being present in the said composition in a proportion by
weight of 5 to 50%. The use of this filler makes it possible, on the one hand, to avoid the
2 0 addition of acrylic polymers to the fluoropolymer and, on the other hand, to use processing
temperatures compatible with the manufacture by blown film extrusion of a monolayer
film, namely of the order of 220 to 260°C, which makes it possible to avoid damage to the
fluoropolymer. The use of zinc oxide makes it possible to obtain a film which is opaque to
ultraviolet and visible radiation at a thickness of 20 urn. It has been found that the use of
2 5 zinc oxide as sole white inorganic filler does not make it possible to obtain a transmission
of less than 30% at wavelengths of the visible region, for fine layers with a thickness of
less than 20 urn. In point of fact, some applications, in particular in the field of
photovoltaic modules, require film thicknesses of less than 20 um.
30 The present invention thus intends to provide fluoropolymeric compositions which make
possible the manufacture of thin films (less than 20 um) which are opaque to UV and
visible radiation and which comprise little or nothing in the way of acrylic polymers.
* 3
To this end, the invention relates, according to a first aspect, to a composition consisting of
at least one fluoropolymer and of two white inorganic fillers, characterized in that the said
fillers are zinc oxide and titanium oxide, in that they are present in a proportion by weight
ranging from 5 to 30% and from 3 to 7.5% respectively (limits included) and in that the
5 said composition additionally comprises up to 5% by weight of acrylic polymer, these
percentages being calculated with respect to the total weight of the composition. The
content by weight of acrylic polymer is thus greater than 0% and less than 5%, with respect
to the total weight of the composition.
10 The invention also relates to the process for producing the said formulation, to the film
obtained from this formulation and to its use in the photovoltaic field as protective film for
a PET substrate used as back protection for photovoltaic panels. More particularly, the
invention relates to a photovoltaic cell, the back panel of which is coated with a film as
described above. According to yet another aspect, the invention relates to the various
15 processes for the manufacture of the abovementioned monolayer film.
The invention will now be described in detail.
According to a first aspect, the invention relates to a polymeric composition comprising at
2 0 least one fluoropolymer and two pigments based on zinc and titanium, the simultaneous
presence of which makes it possible to obtain, for the thin films manufactured from the
said composition, an opaqueness to UV radiation up to a wavelength of 395 nm, while
having a very good opaqueness in the visible region with a transparency of less than 25%
at 450 nm, with excellent thermal stability and a yellowing index (YI) of less than 4. This
2 5 combination of properties is obtained, on the one hand, by virtue of the presence of two
white inorganic fillers, namely zinc oxide and titanium dioxide, and, on the other hand, by
virtue of the limitation of the content of acrylic polymers to less than 5% by weight, with
respect to the total weight of the composition.
30 As regards the fluoropolymer, the latter is prepared by polymerization of one or more
monomer(s) of formula (I):
XI X2
\ / /C=cx <„
F X3
in which:
• XI denotes H or F;
• X2 and X3 denote H, F, CI, a fluoroalkyl group of formula CnFmHp- or a
5 fluoroalkoxy group CnFmHpO-, n being an integer between 1 and 10, m being an
integer between 1 and (2n+l) and p having the value 2n+l-m.
Use may be made, as monomers, of: hexafluoropropylene (HFP),
tetrafluoroethylene (TFE), vinylidene fluoride (VDF, CH2=CF2), chlorotrifluoroethylene
(CTFE), perfluoroalkyl vinyl ethers, such as CF3-0-CF=CF2, CF3-CF2-0-CF=CF2 or
10 CF3-CF2CF2-0-CF=CF2, l-hydropentafluoropropene, 2-hydropentafluoropropene,
dichlorodifluoroethylene, trifluoroethylene (VF3), 1,1-dichlorofluoroethylene and their
mixtures, or fluorine-comprising diolefins, for example diolefins such as perfluorodiallyl
ether and perfluoro-1,3 -butadiene.
The fluoropolymers which may participate in the composition according to the
15 invention are chosen from:
- TFE homo- or copolymers, in particular PTFE (polytetrafluoroethylene), ETFE
(ethylene/tetrafluoroethylene copolymer) and TFE/PMVE (tetrafluoroethylene/-
perfluoro(methyl vinyl) ether copolymer), TFE/PEVE (tetrafluoroethylene/-
perfluoro(ethyl vinyl) ether copolymer), TFE/PPVE (tetrafluoroethylene/
2 0 perfluoro(propyl vinyl) ether copolymer) and E/TFE/HFP (ethylene/-
tetrafluoroethylene/hexafluoropropylene terpolymers) copolymers;
- VDF homo- or copolymers, in particular PVDF and VDF/HFP copolymers;
- CTFE homo- or copolymers, in particular PCTFE (polychlorotrifluoroethylene) and
E/CTFE (ethylene/chlorotrifluoroethylene copolymer).
2 5 Preferably, the fluoropolymer is a VDF homopolymer or a copolymer of VDF and
of at least one other fluoromonomer.
Advantageously, the fluorocomonomer which can copolymerize with the VDF is
chosen, for example, from vinyl fluoride, trifluoroethylene (VF3); chlorotrifluoroethylene
30 (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP);
perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE),
perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE);
perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-l,3-dioxole) (PDD), and their mixtures.
Preferably, the fluorocomonomer is chosen from chlorotrifluoroethylene (CTFE),
hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE), and
5 their mixtures. The comonomer is advantageously HFP as it copolymerizes well with VDF
and makes it possible to contribute good thermomechanical properties. Preferably, the
copolymer comprises only VDF and HFP.
Preferably, the fluoropolymer is a VDF homopolymer (PVDF) or a VDF
copolymer, such as VDF/HFP, comprising at least 50% by weight of VDF, advantageously
10 at least 75% by weight of VDF and preferably at least 90%) by weight of VDF. Mention
may be made, for example, more particularly of the following VDF homopolymers or
copolymers comprising more than 75% of VDF and the remainder of HFP: Kynar® 710,
Kynar®720, Kynar® 740, Kynar Flex® 2850 and Kynar Flex® 3120, sold by Arkema.
Advantageously, the composition according to the invention comprises two distinct
15 fluoropolymers, at least one of which is a VDF homopolymer.
Advantageously, the fluoropolymer has a viscosity ranging from 100 Pa.s to
3000 Pa.s, the viscosity being measured at 230°C at a shear gradient of 100 s"1 using a
capillary rheometer. This is because this type of polymer is well suited to extrusion.
Preferably, the polymer has a viscosity ranging from 500 Pa.s to 2900 Pa.s.
2 0 The first white inorganic filler is zinc oxide (ZnO). It has an opacifying role in
the UV/visible region and acts as sunscreen, so that the film prepared from the composition
according to the invention is a film which is opaque to UV radiation, mainly by
scattering/reflection of the UV rays, but also to visible light.
The ZnO content of the composition is between 5 and 30% by weight,
25 advantageously between 10 and 20% by weight (limits included), with respect to the total
weight of the composition.
The second white inorganic filler is titanium dioxide (Ti02). Like zinc oxide,
titanium oxide has an opacifying role in the UV/visible region and acts as sunscreen, so
that the film prepared from the composition according to the invention is a film which is
3 0 opaque to UV radiation, mainly by scattering/reflection of the UV rays, but also to visible
light.
The TiC>2 content of the composition is between 3 and 7.5% by weight,
advantageously between 3 and 6% by weight (limits included), with respect to the total
weight of the composition.
•
•
The acrylic polymer (or acrylate) is a methyl methacrylate (MMA) homopolymer
or a copolymer comprising at least 50% by weight of MMA and at least one other
monomer which can copolymerize with MMA. Comonomers which can copolymerize with
MMA are alkyl (meth)acrylates, acrylonitrile, butadiene, styrene or isoprene.
5 Advantageously, the acrylic polymer (MMA homopolymer or copolymer)
comprises, by weight, from 0 to 20% and preferably from 5 to 15% of a Q-Cg alkyl
(meth)acrylate, which is preferably methyl acrylate and/or ethyl acrylate. The acrylic
polymer can be functionalized, that is to say that it comprises, for example, acid, acid
chloride, alcohol or anhydride functional groups. Advantageously, the functionality is in
10 particular the acid functional group introduced by the acrylic acid comonomer. Use may
also be made of a monomer comprising two neighbouring acrylic acid functional groups
which can dehydrate to form an anhydride. The proportion of functionality can be from 0
to 15% by weight of the MMA polymer.
The invention also relates to a process for the manufacture of the said composition
15 which comprises several stages. In a first step, a first masterbatch comprising the zinc
oxide (known as "masterbatch A") is prepared by incorporation by the molten route of
ZnO in a fluoropolymer, the viscosity of which is less than 1000 Pa.s at 230°C for a
shearing of 100 s"1. This makes it possible to obtain a good state of dispersion of the zinc
oxide particles in the fluoropolymer. Separately, a second masterbatch (known as
2 0 "masterbatch B"), which is an acrylic masterbatch, is prepared by incorporation by the
molten route of Ti02 in an acrylic matrix. The TiC>2 content of this masterbatch B must be
greater than 50% by weight in order to keep the level of final acrylic polymer below 5%.
The masterbatch A is subsequently dispersed in a more viscous fluorinated matrix
which makes it possible to obtain good mechanical properties, before and after thermal
25 ageing. The masterbatch B is added to this mixture. The product thus obtained is
subsequently extruded, so as to produce the thin films according to the invention.
According to another aspect, a subject-matter of the invention is a monolayer film
manufactured from the composition described above. This film is opaque to UV and
visible radiation while retaining very good properties of dimensional stability at the
3 0 temperatures used for the manufacture of a backsheet and subsequently of a photovoltaic
panel.
The film according to the invention exhibits the following characteristics:
a thickness of less than 20 p.m, preferably of between 15 and 19 urn and
advantageously of between 16 and 18 um (limits included);
- a density of between 1.98 and 2.07 g/cm3 (limits included);
- a weight per unit area of between 29.7 and 41.4 g/m2 (limits included);
- an elongation at break (in %):
o in the machine direction: of between 200 and 300;
5 o in the cross direction: of between 180 and 270;
- a tensile strength (in MPa):
o in the machine direction: of between 20 and 70;
o in the cross direction: of between 10 and 60;
- a dimensional modification after passing to the oven at 150°C for 30 min (in %):
10 o in the machine direction: less than or equal to 0.5;
o in the cross direction: less than or equal to 0.5.
This film is opaque to UV and visible radiation and exhibits a long-term stability,
as shown by the damp heat test at 85°C and 85% humidity for 2000 h and by the UV
ageing test.
15 Advantageously, the film according to the invention does not exhibit an acrylic
odour.
The film according to the invention can be manufactured by blown film extrusion
at a temperature ranging from 220 to 260°C. This technique consists in coextruding,
generally from the bottom upwards, a thermoplastic polymer through an annular die. The
2 0 extrudate is simultaneously drawn longitudinally by a drawing device, usually in the form
of rolls, and inflated with a constant volume of air trapped between the die, the drawing
system and the wall of the tube. The inflated tube is generally cooled by an air blowing
ring at the die outlet.
Advantageously, the nature of the first white inorganic filler (ZnO) and the
2 5 presentation of the second white inorganic filler (Ti02) in an acrylic matrix make it
possible to obtain the film by the blown film extrusion technique at temperatures of
220-260°C without causing damage to the fluoropolymer present in the said composition.
This makes it possible to retain intact the specific properties of this fluoropolymer, namely
its very good resistance to bad weather, to UV radiation and to visible light, and to
3 0 chemicals.
The film can also be manufactured by cast film extrusion; this process consists in
drawing, in air, a sheet or a film of polymer between a flat die and a thermostatically
controlled roll. It makes it possible to manufacture sheets with a thickness of between
0.2 mm and 2 mm and films with a thickness of less than 0.2 mm.
Another method employed to manufacture the film according to the invention is the
solvent casting process. This is a process where pigments and a polymer are placed in
solution. This solution, which comprises the dissolved polymer and the dispersed
pigments, is subsequently deposited on a support. The solvent is subsequently evaporated
5 under vacuum and by heating in order to make possible the formation of the film
comprising the pigments. The support is subsequently removed and the film wound off.
The final thickness of the film depends on the thickness of the solution deposited and on its
solids content.
According to another aspect, a subject-matter of the invention is the use of this film
10 in the manufacture of the backsheet in a photovoltaic panel. To this end, according to one
embodiment, the film according to the invention is first subjected, on both its faces, to a
surface treatment of corona type. Subsequently, it is heat laminated on each side with a
PET sheet coated beforehand with adhesive. One of the faces of the laminate thus obtained
is subsequently pressed against a film of EVA type, the other face of the latter being
15 adhesively bonded to a cleaned glass sheet. This structure can be used as backsheet in a
photovoltaic cell.
The film according to the invention is opaque (low transmission of visible light and
UV rays) and additionally protects against penetration with oxygen. The structure retains
an attractive aesthetic appearance of the film (no yellowing over time) and an excellent
2 0 flame resistance.
The fluoropolymer-based film according to the invention exhibits a good thermal
resistance (low shrinkage in volume when it is subjected to high temperatures) and an
excellent resistance to the solvents present in the glues and adhesives used in the
construction of photovoltaic cells and more particularly of the back panel of the cells. This
2 5 structure is thus perfectly well suited to protecting the back panel of photovoltaic cells
(backsheet).
-
As a result of the simultaneous presence of two white pigments, namely ZnO and
Ti02, the film according to the invention is opaque to UV radiation (up to 395 nm) and
only very slightly transparent in the visible region (the transmission is less than 25% at
30 450 nm), for a film with a thickness of less than 20 vim and exhibiting a density of less
than 2100 kg/m3. The film obtained also exhibits a yellowing index of less than 4.
A better understanding of the present invention will be obtained in the light of the
implementational examples which will follow.
Measurement of the mechanical properties
The elongation at break and the tensile strength in the two directions of the film were
measured according to Standard EN 06074-2.
Dimensional stability test
5 The shrinkage of the film is measured according to Standard ISO 11501. A square piece of
film with dimensions of 20 cm x 20 cm is placed in a ventilated oven at 150°C for 30 min.
The dimensions are subsequently measured again. The shrinkage is then evaluated by the
variation in each of the dimensions, with respect to the initial dimension.
UV ageing test
10 The UV accelerated ageing test is carried out using a QUV tester, the following conditions
being applied to the sample: 8 hours of QUV B 313 (UV-B lamps at 313 nm) at 60°C,
0.89 W/m2/nm, then 4 hours at 45°C, with condensation of water on the sample. This test is
carried for 2000 h.
Damp heat test
15 The test is carried out in a climate-controlled chamber where a temperature of 85°C and a
humidity of 85% are maintained. After 2000 h, the samples are withdrawn and analysed.
Example 1, according to the invention:
Kynar 720 from Arkema (PVDF homopolymer, MFI of 20 at 230°C under 5 kg, viscosity
2 0 of 800 Pa.s at 230°C under shearing of 100 s"1) and zinc oxide (ZnO) with a D50 size of
approximately 1 \im and with a density of 5.6 are blended at a temperature of less than
230°C on a cokneader from Buss of PR 46 type (speed of the cokneader 200 rev/minute
and speed of the take-up screw 60 rev/minute). The blend comprises 60% of Kynar 720
and 40% of zinc oxide. The blend thus produced (masterbatch A) does not exhibit any sign
25 of decomposition after this extrusion stage.
This masterbatch A is blended in a Buss cokneader at 230°C (speed of the cokneader
200 rev/minute and speed of the take-up screw 60 rev/minute) with another homopolymer
from Arkema, Kynar 740 (MFI of 3 at 230°C under 10 kg, viscosity of 2000 Pa.s at 230°C
under 100 s"1), and with an acrylic masterbatch (the masterbatch B, composed of 40% of
3 0 PMMA BS550 from Arkema and of 60% of Ti02 of R960 type). The blend thus produced
comprises 54.2% of Kynar 740, 8.3% of masterbatch B and 37.5% of masterbatch A. Its
composition by weight is as follows: 15% ZnO, 4.98% Ti02 and 3.32% acrylic.
The product thus obtained is subsequently extruded on a blown film extrusion line from Dr
Collin GmbH, Ebersberg, Germany. The extrusion temperature is 240°C and the blow ratio
* 10
is 2.5. The film produced exhibits a width of 250 mm and a thickness of 18 um and a
density of 2.01. This film is completely opaque in the UV region up to 395 nm and exhibits
a transmission of 22% at 450 nm. This film is subsequently laminated on a biaxially
oriented PET with a thickness of 250 um using an adhesive from Bostik, a mixture of
5 HBTS EPS 877 and Boscodur 1621. A thickness of adhesive of 8 um is used and the
laminate is postcrosslinked at 60°C for 60 h. After this stage of curing the adhesive, an
adhesion of 8 N/cm is measured. The laminate obtained is subsequently placed in a
climate-controlled chamber at 85°C and 85% relative humidity. No delamination is
obtained and no yellowing is observed after ageing for 2000 h. This same laminate, after a
10 UV ageing test as described above, does not exhibit any yellowing.
Example 2, according to the invention:
Kynar 720 from Arkema (PVDF homopolymer, MFI of 20 at 230°C under 5 kg, viscosity
of 800 Pa.s at 230°C under shearing of 100 s"1) and zinc oxide (ZnO) with a D50 size of 1
15 approximately 1 jam and with a density of 5.6 are blended at a temperature of less than
230°C on a cokneader from Buss of PR 46 type (speed of the cokneader 200 rev/minute
and speed of the take-up screw 60 rev/minute). The blend comprises 60% of Kynar 720
and 40% of zinc oxide. The blend thus produced (masterbatch A) does not exhibit any sign
of decomposition after this extrusion stage.
20 This masterbatch A is blended in a Buss cokneader at 230°C (speed of the cokneader
200 rev/minute and speed of the take-up screw 60 rev/minute) with another homopolymer
from Arkema, Kynar 740 (MFI of 3 at 230°C under 10 kg, viscosity of 2000 Pa.s at 230°C
under 100 s"1), and with a masterbatch B, composed of 40% of PMMA BS550 from
Arkema and of 60% of Ti02 of R960 type. The blend thus produced comprises 50.8% of
25 Kynar 740, 11.7% of masterbatch B and 37.5% of masterbatch A. Its composition by
weight is as follows: 15% ZnO, 7.02% Ti02 and 4.68% acrylic.
The product thus obtained is subsequently extruded on a blown film extrusion line from Dr
Collin GmbH. The extrusion temperature is 240°C and the blow ratio is 2.5. The film
produced exhibits a width of 250 mm and a thickness of 18 um and a density of 2.02. This
30 film is completely opaque in the UV region up to 395 nm and exhibits a transmission of
18% at 450 nm. This film is subsequently laminated on a biaxially oriented PET with a
thickness of 250 um using an adhesive from Bostik, a mixture of HBTS EPS 877 and
Boscodur 1621. A thickness of adhesive of 8 nm is used and the laminate is
postcrosslinked at 60°C for 60 h. After this stage of curing the adhesive, an adhesion of
8 N/cm is measured. The laminate obtained is subsequently placed in a climate-controlled
chamber at 85°C and 85% relative humidity. After 2000 h, no delamination is obtained and
no yellowing is observed. This same laminate, after a UV ageing test as described above,
does not exhibit any yellowing.
5
Example 3, comparative:
Kynar 720 from Arkema (PVDF homopolymer, MFI of 20 at 230°C under 5 kg, viscosity
of 800 Pa.s at 230°C under shearing of 100 s"1) and zinc sulphide (ZnS) with a D50 size of
approximately 1 \im and with a density of 4.09 are blended at a temperature of less than
10 230°C on a cokneader from Buss of PR 46 type (speed of the cokneader 200 rev/minute
and speed of the take-up screw 60 rev/minute). The blend comprises 60% of Kynar 720
and 40% of zinc sulphide. The blend thus produced (masterbatch A') does not exhibit any
sign of decomposition after this extrusion stage.
This masterbatch A' is blended in a Buss cokneader at 230°C (speed of the cokneader
15 200 rev/minute and speed of the take-up screw 60 rev/minute) with another homopolymer
from Arkema, Kynar 740 (MFI of 3 at 230°C under 10 kg, viscosity of 2000 Pa.s at 230°C
under 100 s"1). The blend thus produced comprises 50% of Kynar 740 and 50% of
masterbatch A'. The product thus obtained is subsequently extruded on a blown film
extrusion line from Dr Collin GmbH. The extrusion temperature is 240°C and the blow
2 0 ratio is 2.5. The film produced exhibits a width of 250 mm and a thickness of 18 urn and a
density of 2.00. This film is completely opaque in the UV region up to 375 nm and exhibits
a transmission of 18% at 450 nm. This film is subsequently laminated on a biaxially
oriented PET with a thickness of 250 um using an adhesive from Bostik, a mixture of
HBTS EPS 877 and Boscodur 1621. A thickness of adhesive of 8 urn is used and the
2 5 laminate is postcrosslinked at 60°C for 60 h. After this stage of curing the adhesive, an
adhesion of 8 N/cm is measured. The laminate obtained is subsequently placed in a
climate-controlled chamber at 85°C and 85% relative humidity. After 2000 h, no
delamination is obtained and no yellowing is observed. This same laminate, after a UV
ageing test as described above, has completely lost it opaqueness in the visible and UV
3 0 regions and a strong yellowing is observed.

CLAIMS
1. Composition consisting of at least one fluoropolymer and of two white inorganic
fillers, characterized in that the said fillers are zinc oxide and titanium oxide, in that
5 they are present in a proportion by weight ranging from 5 to 30% and from 3 to
7.5% respectively and in that the said composition additionally comprises up to 5%
by weight of acrylic polymer, with respect to the total weight of the composition.
2. Composition according to Claim 1, in which the said at least one fluoropolymer is
chosen from vinylidene fluoride homopolymers and copolymers of vinylidene
10 fluoride and of at least one other fluoromonomer.
3. Composition according to either of Claims 1 and 2, in which there are two distinct
fluoropolymers, at least one of which is a vinylidene fluoride homopolymer.
4. Composition according to any one of Claims 1 to 3, in which the content by weight
of zinc oxide ranges from 10 to 20%.
15 5. Composition according to any one of Claims 1 to 4, in which the content by weight
of titanium oxide ranges from 3 to 6%.
6. Composition according to any one of Claims 1 to 5, in which the said acrylic
polymer is a methyl methacrylate homopolymer or a copolymer comprising at least
50%) by weight of methyl methacrylate and at least one other monomer which can
2 0 copolymerize with methyl methacrylate chosen from: alkyl (meth)acrylates,
acrylonitrile, butadiene, styrene and isoprene.
7. Monolayer film consisting of the composition according to one of Claims 1 to 6,
having a thickness of less than 20 microns, preferably of between 15 and 19
microns and advantageously between 16 and 18 microns.
25 8. Film according to Claim 7, exhibiting an opaqueness to UV radiation and a
transparency of less than 25%) at 450 nm.
9. Film according to either of Claims 7 and 8, exhibiting a long-term stability, as
shown by the damp heat test at 85°C and 85%) humidity for 2000 h and by the QUV
ageing test.
30 10. Photovoltaic panel, in which the backsheet comprises a film according to one of
Claims 7 to 9.
11. Use of the film according to one of Claims 7 to 9 in the manufacture of the
backsheet in a photovoltaic panel.
12. Process for the preparation of the composition according to one of Claims 1 to 6,
the said process comprising the following stages:
i) a stage of incorporation by the molten route of the zinc oxide in a fluoropolymer
having a viscosity of less than lOOO'Pa.s at 230°C for a shearing of 100 s"', in order to
5 obtain a masterbatch A;
ii) a stage of incorporation by the molten route of the titanium oxide in an acrylic
matrix, the Ti02 content of this blend being greater than 50% by weight, in order to
obtain a masterbatch B, and
iii) a stage of dispersion of the said masterbatch A in a more viscous fluorinated matrix
10 than that of stage i), the masterbatch B being added to this blend.
13. Process for the manufacture of the monolayer film according to one of Claims 7 to 9
by blown film extrusion at a temperature ranging from 220 to 260°C.
14. Process for the manufacture of the monolayer film according to one of Claims 7 to 9
by cast film extrusion.
15 15. Process for the manufacture of the monolayer film according to one of Claims 7 to 9
by solvent casting.
•Dated this 01/04/2013 wl
(SHRIMANT SINGH)