Multilayer film with polyamide and polyester layers for the production of photovoltaic modules

1. A multilayer film, comprising, in the order listed:

a) a first layer of from 15 to 100 μm in thickness having a composition which comprises a light reflecting filler and at least 35% by weight of polyamide based on the weight of the composition of the first layer;

c) a second layer of from 100 to 500 μm in thickness having a composition which comprises a polyamide, at least one of a reinforcing filler and a light reflecting filler and at least 35% by weight of a thermoplastic polyester based on the weight of the composition of the second layer;

e) a third layer of from 15 to 100 μm in thickness having a composition which comprises at least one of a reinforcing filler and a light reflecting filler and at least 35% by weight of polyamide based on the weight of the composition of the third layer;

wherein

the thickness of the first layer is independent of the thickness of the third layer,

the compositions of the first and third layers each further comprise 0.1 to 60% by weight of a polyamine-polyamide graft copolymer, or

the composition of the second layer further comprises 0.1 to 30% by weight of polyamine-polyamide graft copolymer;

with the proviso that the polyamine-polyamide graft copolymer comprises as copolymerized monomers:

0.5 to 25% by weight, based on the weight of the graft copolymer, of a polyamine having at least 4 nitrogen atoms and

at least one polyamide-forming unit selected from the group consisting of a lactam, an ω-aminocarboxylic acid and an equimolar combination of a diamine and a dicarboxylic acid.

2. The multilayer film according to claim 1 wherein the thermoplastic polyester of the second layer is a linear polyester comprising polycondensed diols and dicarboxylic acids or polyester-forming derivatives thereof wherein

the diol is of formula

HO—R—OH

wherein R is a divalent branched or unbranched aliphatic and/or cycloaliphatic radical having 2 to 40 carbon atoms, and

the dicarboxylic acid is of formula

HOOC—R′—COOH

wherein R′ is a divalent aromatic radical having 6 to 20 carbon atoms.

3. The multilayer film according to claim 1 , wherein

the polyamide present in at least 35% of each of the first and third layers comprises independently one selected from the group consisting of a partly crystalline polyamide having an enthalpy of fusion of more than 25 J/g, a semicrystalline polyamide having an enthalpy of fusion of from 4 to 25 J/g and an amorphous polyamide having an enthalpy of fusion of less than 4 J/g.

4. The multilayer film according to claim 1 wherein the polyamide present in at least 35% of the first layer, the polyamide present in at least 35% of the third layer or both the polyamides present in at least 35% of the first layer and the third layer comprises at least one of a polyetheresteramide and a polyetheramide.

5. A photovoltaic module, comprising;

a solar cell embedded in a sealing layer; and

the multilayer film according to claim 1 as a back cover;

wherein the first layer of the multilayer film is bonded to the sealing layer.

6. The photovoltaic module according to claim 5 , wherein at least one of the first layer, the third layer and the second layer further comprises an impact-modifying rubber optionally modified with a polyamide compatible functional group.

7. The multilayer film of claim 1 , further comprising:

b) optionally, an adhesion promoter layer between the first and second layer; and

d) optionally, an adhesion promoter layer between the second and third layer;

wherein

at least one adhesion promoter layer is present, and

comprises:

0.1 to 100% by weight of a polyamine-polyamide graft copolymer,

0 to 99.9% by weight of a polyamide and

0 to 99.9% by weight of a thermoplastic polyester,

with the proviso that the polyamine-polyamide graft copolymer comprises as copolymerized monomers:

0.5 to 25% by weight, based on the weight of the graft copolymer, of a polyamine having at least 4 nitrogen atoms and

at least one polyamide-forming unit selected from the group consisting of a lactam, an ω-aminocarboxylic acid and an equimolar combinations of a diamine and a dicarboxylic acid.

8. The multilayer film according to claim 7 , wherein the polyamine of the graft copolymer is one selected from the group consisting of a polyvinylamine, a polyamine prepared from an alternating polyketone, a dendrimer, a linear polyethyleneimine, and a branched polyethyleneimine.

9. The multilayer film according to claim 8 wherein a number average molecular weight of the polyamine is not greater than 20,000 g/mol.

10. A photovoltaic module, comprising;

a solar cell embedded in a sealing layer; and

the multilayer film according to claim 7 as a back cover;

wherein the first layer of the laminate film is bonded to the sealing layer.

11. The multilayer film of claim 1 , wherein at least one of the second layer c) and the third layer e) comprise a reinforcing filler.

12. The multilayer film of claim 1 , wherein the second layer c) and the third layer e) comprise a reinforcing filler.

13. The multilayer film of claim 1 , wherein at least one of the second layer c) and the third layer e) comprise a reinforcing filler and the reinforcing filler is glass fibers.

14. The multilayer film of claim 1 , wherein the second layer c) and the third layer e) comprise a reinforcing filler and the reinforcing filler is glass fibers.