Patent ID: 8632876

Claim:
A laminated polyester film for solar cell backsheets, the laminated film comprising a surface layer (A) and a substrate layer (B), and characterized in that: the surface layer (A) is provided on at least one side of the substrate layer (B); the surface layer (A) is made of a polyester composition including 10 to 30 wt % of rutile-type titanium dioxide particles and 70 to 90 wt % of a polyester; the substrate layer (B) is made of a polyester composition including 0.1 to 4 wt % of rutile-type titanium dioxide particles and 96 to 99.9 wt % of a polyester; the substrate layer (B) has a thickness of 70% to 97% of the total film thickness; the weight average molecular weight of polyester in the laminated film is 47000 to 65000; the COOH end group concentration of polyester in the laminated film is 6 to 25 eq/ton; and the average content of rutile-type titanium dioxide particles in all layers of the laminated film is 3 to 8 wt %, wherein the average content of rutile-type titanium dioxide particles in all layers is defined by the following equation: average content of rutile-type titanium dioxide particles in all layers (wt %)=content of rutile-type titanium dioxide particles in the surface layer (A)(wt %)×(thickness of the surface layer (A)/total film thickness)+content of rutile-type titanium dioxide particles in the substrate layer (B)(wt %)×(thickness of the substrate layer (B)/total film thickness).