Magnetic tape, method of cleaning the same, and apparatus for forming and cleaning optical servo tracks

Abstract

A magnetic tape which comprises a nonmagnetic support, a magnetic layer which is formed on one surface of the nonmagnetic support, and a backcoat layer which comprises a binder and nonmagnetic powder containing carbon black as a component and which is formed on the other surface of the nonmagnetic support, having pits for optical servo formed thereon, characterized in that the average of the reflectance on the flat portion of the backcoat layer is 8.5% or higher, and that the maximum rate of fluctuation of the reflectance on the flat portion, depending on a position of the magnetic tape: [Maximum of absolute value of(Reflectance−Average reflectance)]×100/(Average reflectance) is 10% or lower. This magnetic tape is high in the initial S/N of the servo signal, and also high in the S/N of the servo signal found after the magnetic tape is run twice.

1 . A method for cleaning a magnetic tape which comprises a nonmagnetic support, a magnetic layer which is formed on one surface of the nonmagnetic support, and a backcoat layer which contains nonmagnetic powder and a binder and which is formed on the other surface of the nonmagnetic support, having pits for optical servo formed thereon by irradiation with laser beams, said method comprising the step of allowing a raised fabric or a woven or nonwoven cloth having raising fibers thereon to contact with the surface of the backcoat layer having the pits formed thereon, thereby removing burnt residues adhered to the pits and their peripheries, and wiping the surfaces of the magnetic tape. 
     
     
         2 . The method according to  claim 1 , wherein said raising fiber is a single fiber having a diameter of 0.5 to 10 μm and a length of 0.5 to 5 mm. 
     
     
         3 . The method according to  claim 1 , wherein said raising fiber is at least one selected from natural fibers and synthetic fibers. 
     
     
         4 . The method according to  claim 2 , wherein said raising fiber is at least one selected from natural fibers and synthetic fibers. 
     
     
         5 . The method according to  claim 1 , wherein said raising fiber contains cotton. 
     
     
         6 . The method according to  claim 1 , wherein the burnt residues adhered to the pits for optical servo and their peripheries on the surface of the backcoat layer are raked out and removed by rotating or moving the raised fabric or the woven or nonwoven cloth having the raising fibers thereon in a direction reverse to the magnetic tape-running direction.