Flame-retardant biaxially oriented polyester film, and flame-retardant polyester film laminate comprising the same and flexible circuit board

A flame-retardant biaxially oriented polyester film consisting essentially of, based on the weight of the polyester film, 70 to 99% by weight of polyethylene terephthalate or polyethylene naphthalate, and 1 to 30% by weight of flame retardant particles having an average particle diameter of 1.5 to 3.0 μm and being represented by the following formula (1) or formula (2):

• wherein each of R1 and R2 represents hydrogen, an alkyl group having 1 to 6 carbon atoms and/or an aryl group, M represents a metal, and m represents a valence of M,
• wherein each of R3 and R4 represents hydrogen, an alkyl group having 1 to 6 carbon atoms and/or an aryl group, R5 represents an alkylene group having 1 to 6 carbon atoms or an arylene group, allcylarylene group, or arylalkylene group having 6 to 10 carbon atoms, M represents a metal, and n represents a valence of M,
• wherein the biaxially oriented polyester film has an Rmax (maximum height) of 1.8 μm to less than 3 μm,
• wherein the flame-retardant biaxially oriented polyester film has a surface roughness Ra of 0.1 to less than 0.5 μm.
• wherein the flame-retardant biaxially oriented polyester film has a mechanical strength of 150 MPa or more,
• wherein the number of coarse particles having a maximum length of 10 μm or more contained in the polyester film is 10/m2 or less.