Polyester film for magnetic recording media and magnetic recording tape

Abstract

A polyester film for magnetic recording media includes a coating layer containing fine particles and organic compounds formed on surface A at one side of the polyester film, and fine surface protrusions formed at a density of 3×10 6 to 1×10 8 protrusions/mm 2 on surface A. The polyester film satisfies at least one of the following conditions: (a) the mean diameter of the fine surface protrusions is in the range of 5 to 60 nm, and, among the fine surface protrusions, the density of fine surface protrusions with a height of 20 nm or more is 3,000 protrusions/mm 2 , and (b) the mean diameter of the fine surface protrusions is in the range of 5 to 100 nm, the mean height of the fine surface protrusions is in the range of 5 to 30 nm, and the degree of cohesion of the fine surface protrusion is less than 15%.

1 . A polyester film for magnetic recording media comprising a coating layer containing fine particles and organic compounds and having a surface A formed on one side of the polyester film, fine surface protrusions being formed at a density of 5×10 6  to 9×10 7  protrusions/mm 2  on surface A, the polyester film satisfying the following conditions: 
 (1) the mean diameter of the fine surface protrusions is in the range of 20 to 100 nm,    (2) the mean height of the fine surface protrusions is in the range of 10 to 30 nm, and    (3) the degree of cohesion of the fine surface protrusions is less than 5%.    
     
     
         2 . The polyester film for magnetic recording media according to  claim 1 , wherein the surface roughness of surface A is in the range of 1 to 5 nm.  
     
     
         3 . The polyester film for magnetic recording media according to  claim 1 , wherein the fine particles are organic polymer particles.  
     
     
         4 . The polyester film for magnetic recording media according to  claim 1 , wherein the polyester is polyethylene terephthalate or polyethylene-2,6-naphthalate.  
     
     
         5 . A magnetic recording tape comprising the polyester film according to  claim 1  and a ferromagnetic metal thin layer formed on surface A.  
     
     
         6 . A magnetic recording tape according to  claim 5 , wherein the thickness of the ferromagnetic metal thin layer is 20 to 70 nm.  
     
     
         7 . The polyester film for magnetic recording media according to  claim 1 , wherein (a) the mean diameter of the fine surface protrusions is in the range of 5 to 60 nm, and, among the fine surface protrusions, the density of fine surface protrusions with a height of 20 nm or more is 3,000 protrusions/mm 2  or less.