Multilayer, biaxially oriented polyester film, process for its production and its use as a magnetic tape film without a backing coating

A biaxially oriented, coextruded, at least three-layer polyester film, the at least three layers being mainly composed of polyester, the two surfaces of which film are formed by outer layers A and C, a base layer B being present between these outer layers, wherein the outer layer A

• has a number of protuberances/projections Na
• per 0.36 mm2 which is related to their
• respective heights ha as follows:
• A1·e−B1·ha≦Na≦A2·e−B2·ha (1)
• where A1=300, A2=7000
• B1=7.0, B2=8.0 and
• 0.01 μm <hA<1.0 μm and the outer layer C
• has an Ra value which is greater than that of the outer layer A and a
• number of protuberances/projections Nc per 0.36 mm2 which is related to their respective heights hc as follows:
• Nc<F2·e−G2·hc (3)
• where F2=12,000
• G2=12.0
• 0.01 μm ≦hc<1.0 μm and the gas flow in the roughness profile of the surface of outer layer C is >550 sec.