Patent ID: 8318289

Claim:
A composite film comprising a heat-stabilised, heat-set, oriented poly(ethylene naphthalate) substrate, and a coating layer having a surface; wherein said substrate exhibits one or more of: (i) a shrinkage at 30 mins at 230° C. of less than 1%; and/or (ii) a residual dimensional change ΔL r measured at 25° C. before and after heating the substrate from 8° C. to 200° C. and then cooling to 8° C., of less than 0.75% of the original dimension; and/or (iii) a coefficient of linear thermal expansion (CLTE) within the temperature range from −40° C. to +100° C. of less than 40×10 −6 /° C.; and wherein the surface of said coating layer exhibits an Ra value of less than 0.6 nm, and/or an Rq value of less than 0.8 nm, the thickness of the substrate is between 50 and 250 μm and wherein the number of surface peaks in the range 300 to 600 nm per 5 cm 2 area (N(300-600)) of the film is less than 50.