Photovoltaic module backsheet comprising polyolefin layers

1 . A coextruded photovoltaic module backsheet comprising a functional layer and a weather-resistant layer, wherein the backsheet is free of fluorinated polymers, characterized in that:

i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50 wt. % of the functional layer is polyethylene, and wherein the polyethylene copolymer is an ethylene acrylate copolymer from 1 to 40% wt.; and

ii) the weather-resistant layer comprises, a first sub-layer facing the functional layer and a second sub-layer, wherein

a) each of the first sub-layer and the second sub-layer comprise at least 50 wt. % polypropylene; and

b) the second sub-layer has a lowest glass transition temperature (T g ) below −40° C.,

wherein the second sub-layer comprises from 20 wt. % to 40 wt. % polyolefin elastomer.

2 . The photovoltaic module backsheet according to claim 1 , wherein the second sub-layer has a lowest glass transition temperature (T g ) at least 20° C. lower than the lowest glass transition temperature (T g ) of the first sub-layer.

3 . The photovoltaic module according to claim 1 , wherein the weather-resistant layer comprises, in order, a first sub-layer, a second sub-layer and a third sub-layer, wherein the third sub-layer comprises at least 50 wt. % polypropylene.

4 . The photovoltaic module according to claim 3 , wherein the second sub-layer has a lowest glass transition temperature (T g ) at least 20° C. lower than the lowest glass transition temperature (T g ) of the third sub-layer.

5 . The photovoltaic module backsheet according to claim 3 , wherein each of the first sub-layer and the third sub-layer comprise from 70 wt. % to 90 wt. % polypropylene.

6 . The photovoltaic module backsheet according to claim 3 , wherein the first sub-layer and the third sub-layer have an identical chemical composition.

7 . The photovoltaic module backsheet according to claim 1 , wherein the second sub-layer comprises a blend of polypropylene with a polyolefin elastomer.

8 . The photovoltaic module backsheet according to claim 1 , which further comprises a connecting layer, located between the functional layer and the weather-resistant layer.

9 . The photovoltaic module backsheet according to claim 1 , wherein functional layer comprises a ternary blend of polypropylene, polyethylene and a polyethylene copolymer.

10 . The photovoltaic module backsheet according to claim 1 , wherein the functional layer has a thickness of from 10 to 50 μm.

11 . The photovoltaic module backsheet according to claim 1 , wherein the weather-resistant layer has a thickness of from 100 to 500 μm.

12 . The photovoltaic module comprising a photovoltaic module backsheet as defined in claim 1 .

13 . A process for producing a photovoltaic module backsheet as defined in claim 1 comprising:

i) feeding the functional layer composition, the first sub-layer composition, the second sub-layer composition and, where present, a third sub-layer composition to a multi-layer film coextrusion apparatus; and

ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order: functional layer, first sub-layer, second sub-layer and, where present, third sub-layer.

14 . A process according to claim 13 comprising:

i) feeding the functional layer composition, a connecting layer composition, the first sub-layer composition, the second sub-layer composition and a third sub-layer composition to a multi-layer film coextrusion apparatus; and

ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order: functional layer, connecting layer, first sub-layer, second sub-layer, third sub-layer.