Multiple-layer backcoating for magnetic tape

Abstract

A magnetic tape comprises a substrate having on one side thereof a magnetic layer serving as a recording surface, and on the other side thereof at least two layers containing inorganic particles which serve as a non-recording surface, wherein said magnetic tape has a region on the side of the non-recording surface along the longitudinal direction of the tape in which a regular pattern for servo tracking having different optical properties from the other major region of the side of the non-recording surface is or can be formed. The layers on the non-recording surface are characterized in that the inorganic particles in the outermost layer are larger than the inorganic particles in the underlying layer(s).

What is claimed is:  
     
         1 . A magnetic tape comprising a substrate having disposed on opposite sides thereof a recording surface and a non-recording surface, wherein the recording surface comprises a magnetic layer, and the non-recording surface comprises at least two layers containing inorganic particles, said two layers comprising a first outer layer and a second inner layer, wherein the first layer comprises inorganic particles of a size sufficient to provide improved tape runnability and conductivity and to reduce reflectance, and the inner layer comprises inorganic particles of a size different from the inorganic particles in the first layer, wherein the size of the inorganic particles in the second layer provide improved servo cutting quality to the tape.  
     
     
         2 . The magnetic tape of  claim 1  wherein the inorganic particles in the first layer are larger than the inorganic particles in the second layer.  
     
     
         3 . The magnetic tape of  claim 1  wherein the non-recording surface has disposed along a longitudinal direction of the tape a regular pattern for servo tracking, said pattern having optical properties different from the non-patterned region of the non-recording surface.  
     
     
         4 . The magnetic tape of  claim 1  wherein said optical properties comprises an absorbance, reflectance or transmission of light, and the difference between said pattern and the non-patterned region of the non-recording surface in absorbance, reflectance or transmission of light having a prescribed wavelength used for servo tracking is about 10% or more.  
     
     
         5 . The magnetic tape of  claim 1 , wherein the inorganic particles are carbon black particles.  
     
     
         6 . The magnetic tape of  claim 1  wherein the size of the particles in the first outer layer is in the range of from about 0.05 μm to about 0.08 μm.  
     
     
         7 . The magnetic tape of  claim 1  wherein the size of the particles in the second inner layer is in the range of from about 0.02 μm to about 0.035 μm.  
     
     
         8 . The magnetic tape of  claim 1  wherein said magnetic tape further comprises a layer of a metal or a metal alloy having a low melting point disposed between said substrate and said second layer, and a servo tracking pattern comprising depressions is formed in said metal or alloy layer.  
     
     
         9 . The magnetic tape of  claim 8  wherein said servo tracking pattern has a width of from about 0.1 to about 30 μm and a depth of from about ⅓ of the thickness of said metal or alloy layer up to the entire thickness of said thin layer.  
     
     
         10 . A magnetic tape comprising a substrate having disposed on opposite sides thereof a recording surface, and a non-recording surface, wherein the recording surface comprises a magnetic layer, and the non-recording surface comprises at least two layers containing inorganic particles, wherein said magnetic tape has a regular pattern for servo tracking on the non-recording surface along the longitudinal direction of the tape which pattern has optical properties which differ from the non-patterned region of the non-recording surface.  
     
     
         11 . A magnetic tape comprising a substrate having on one side thereof a recording surface comprising a magnetic layer, and on the other side thereof a backcoat system of at least two layers comprising a first outer layer and a second inner layer containing carbon black particles, wherein said backcoat system has disposed along the longitudinal direction of the tape a regular pattern for servo tracking having optical properties different from the non-patterned region.  
     
     
         12 . A magnetic tape according to  claim 11 , wherein 
 the regular pattern comprises a repeating pattern of marks extending along substantially the length of the tape.    
     
     
         13 . The magnetic tape according to  claim 11 , wherein 
 the regular pattern comprises a repeating pattern of marks extending transversely to an axis substantially perpendicular to the longitudinal edge of the tape.    
     
     
         14 . A method of making a recording tape, comprising the steps of 
 providing a substrate having disposed on one side thereof a magnetic layer serving as a recording surface and on the other side thereof a backcoating system comprising a first outer layer and a second inner layer containing inorganic particles, and    directing a beam of light at said backcoat layer thereby to form an optically detectable depression in said backcoat layer.    
     
     
         15 . A method according to  claim 14 , further comprising the step of forming a plurality of depressions in the layer.