Single- or multilayer, stabilized polyester film

A polyester film comprising at least one UV stabilizer of the formula I,

• wherein
• R1 is hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkenyl, heterocycloalkyl, aryl, or heteroaryl, and
• R2 is a moiety which contains at least one π-electron system, which contains a carbon atom and at least one further atom selected from carbon, oxygen, and nitrogen, where the moiety R2 contains at least one atom different from carbon;
• and
• wherein
• the film-thickness-standardized concentration of said UV stabilizer(s) of formula I (CnI), when two or more different compounds of formula I are used CnI means the total concentration of all of the compounds of formula I, in said film complies with the following Equation 1:
• CnI=CI·d Equation 1
• where
• d=film thickness in μm;
• CI=total concentration of all of the compounds of formula I in said film in % by weight;
• CnI=standardized total concentration of all of the compounds of formula I in said film in % by weight·μm
• and is CnI≧4% by weight·μm and ≦60% by weight·μm;
• said film comprising at least one further UV absorber which does not correspond to the formula I having at least one absorption maximum above 340 nm, present in an amount of 5 to 400 by weight based on of the amount of Formula I,
• wherein the F5 values (force at 5% tensile strength of said film), longitudinally (MD) and transversely (TD) are >70 N/mm2 and said film does not visibly fluoresce within the visible region from 400 to 700 nm.