Polyethylene-2,6-naphthalenedicarboxylate film

A biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film which satisfies the following expressions (1)-(3),

• 1,500.ltoreq.M.sub.1 .ltoreq.20,000 pieces/mm.sup.2 ( 1)
• 5.ltoreq.M.sub.2 .ltoreq.200 pieces/mm.sup.2 ( 2)
• 0.ltoreq.M.sub.3 .ltoreq.50 pieces/mm.sup.2 ( 3)
• wherein when h (unit:
• nm) stands for a height of a protrusion formed on the film surface, M.sub.1 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 1.ltoreq.h<50, M.sub.2 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 50.ltoreq.h<100, and M.sub.3 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 100.ltoreq.h,
• the film having a Young's modulus (EM) of at least 600 kg/mm.sup.2 in the longitudinal direction and a Young's modulus (ET) of 600-1,100 kg/mm.sup.2 in the transverse direction,
• the film having a plane orientation coefficient NS and an average refractive index n.sub.a which satisfy the following expression
• NS.ltoreq.1.607n.sub.a -2.434, (4)
• the film having a surface roughness (Ra) of 2-10 nm, a thickness of 50 .mu.m or less and having a heat shrinkage in the longitudinal direction of 0.08% or less when treated under no load at 70.degree. C. for 1 hour.

A magnetic recording medium comprising a

• biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film which satisfies the following expressions (1)-(3),
• 2,000.ltoreq.M.sub.1 .ltoreq.20,000 pieces/mm.sup.2 ( 1)
• 10.ltoreq.M.sub.2 .ltoreq.150 pieces/mm.sup.2 ( 2)
• 0.ltoreq.M.sub.3 .ltoreq.40 pieces/mm.sup.2 ( 3)
• wherein when h (unit:
• nm) stands for a height of a protrusion formed on the film surface, M.sub.1 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 1.ltoreq.h<50, M.sub.2 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 50.ltoreq.h<100, and M.sub.3 (unit:
• pieces/mm.sup.2) is the number of protrusions in the range of 100.ltoreq.h,
• the film having a Young's modulus (EM) of at least 600 kg/mm.sup.2 in the longitudinal direction and a Young's modulus (ET) of 600-1,100 kg/mm.sup.2 in the transverse direction,
• the film having a plane orientation coefficient NS and an average refractive index n.sub.a which satisfy the following expression
• NS.gtoreq.1.607n.sub.a -2.434, (4)
• the film having a surface roughness (Ra) of 5-10 nm, a thickness of 25 .mu.m or less and having a heat shrinkage in the longitudinal direction of 0.08% or less when treated under no load at 70.degree. C. for 1 hour, and
• having a magnetic recording layer on at least one surface of said film.