Rubber-steel cord composite and pneumatic tire for passenger cars

Abstract

A rubber-steel cord composite comprising a steel cord having, in a planar image of the steel cord formed by X-rays passing through the steel cord, a fraction R of the total area occupied by filaments of from 0.45 or more to 0.95 or less in an arbitrarily selected portion of the steel cord having a length of 15 mm in an axial direction of the cord, is provided. The length of 15 mm in an axial direction of the cord means a length of 15 mm in an axial direction of an actual cord and the fraction R of the total area occupied by the filaments is expressed as R=F/A, wherein A represents the total area of the cord and F represents the area of the cord occupied by the filaments. An object of the present invention is to provide a pneumatic tire for passenger cars that shows no separation at the interface of adhesion during use, particularly during use in the run-flat condition, and exhibits excellent durability.

What is claimed is:  
     
         1 . A rubber-steel cord composite comprising a steel cord having, in a planar image of the composite formed by X-rays passing through the composite, a fraction R of the total area occupied by filaments of from 0.45 or more to 0.95 or less in an arbitrarily selected portion of the steel cord having a length of 15 mm in an axial direction of the cord, 
 wherein the length of 15 mm in an axial direction of the cord means a length of 15 mm in an axial direction of an actual cord and the fraction R of the total area occupied by the filaments is expressed as R=F/A, A representing the total area of the cord and F representing the area of the cord occupied by the filaments.    
     
     
         2 . A rubber-steel cord composite according to  claim 1 , wherein the filaments of the steel cord are present substantially independently of each other in a matrix rubber.  
     
     
         3 . A rubber-steel cord composite according to  claim 1 , wherein the steel cord has one of a 1×n structure and a 1+n structure, n being in a range of 2≦n≦7.  
     
     
         4 . A rubber-steel cord composite according to  claim 1 , wherein the filament constructing the steel cord has a diameter in a range of from 0.125 to 0.275 mm.  
     
     
         5 . A pneumatic tire for passenger cars comprising a rubber-steel cord composite which comprises a steel cord having, in a planar image of the composite formed by X-rays passing through the composite, a fraction R of the total area occupied by filaments of from 0.45 or more to 0.95 or less in an arbitrarily selected portion of the steel cord having a length of 15 mm in an axial direction of the cord, 
 wherein the length of 15 mm in an axial direction of the cord means a length of 15 mm in an axial direction of an actual cord and the fraction R of the total area occupied by the filaments is expressed as R=F/A, A representing the total area of the cord and F representing the area of the cord occupied by the filaments.    
     
     
         6 . A pneumatic tire for passenger cars according to  claim 5 , wherein the filaments of the steel cord are present substantially independently of each other in a matrix rubber.  
     
     
         7 . A pneumatic tire for passenger cars according to  claim 5 , wherein the steel cord has one of a 1×n structure and a 1+n structure, n being in a range of 2≦n≦7.  
     
     
         8 . A pneumatic tire for passenger cars according to  claim 5 , wherein the filament constructing the steel cord has a diameter in a range of from 0.125 to 0.275 mm.  
     
     
         9 . A pneumatic tire for passenger cars according to  claim 5 , wherein the rubber-steel cord composite is used in a carcass layer of the pneumatic tire.  
     
     
         10 . A pneumatic tire for passenger cars according to  claim 5 , further comprising a side wall portion reinforced with a rubber reinforcing layer.  
     
     
         11 . A pneumatic tire for passenger cars according to  claim 9 , wherein the carcass comprises: a turned-up ply reinforced with a cord of an organic fiber having a melting point of 245° C. or higher, and 
 a down carcass ply comprising a rubber-steel cord composite in which a plurality of steel cords disposed substantially parallel to each other is embedded in a matrix rubber, said down carcass ply being disposed between a side wall rubber and an outer face of the turned-up ply.  
 
     
     
         12 . A pneumatic tire for passenger cars according to  claim 5 , comprising 
 a carcass ply reinforced with polyester cords and/or polyamide cords; wherein    the rubber-steel cord composite is disposed in a side wall portion, the composite in which a plurality of steel cords disposed substantially parallel to each other is embedded in a matrix rubber.    
     
     
         13 . A pneumatic tire for passenger cars according to  claim 9 , wherein the carcass comprises a turned-up ply and a down ply, and the down ply comprises a plurality of steel cords disposed substantially parallel to each other and a matrix rubber, and is disposed between a side wall portion and an outer face of the turned-up ply, and any one of the turned-up ply and the down ply is a separate-type carcass ply which is separated into portions underneath a belt portion.  
     
     
         14 . A pneumatic tire for passenger cars according to  claim 13 , wherein any one of the turned-up ply and the down ply is separated into portions disposed under the belt portion with a distance of at least 20% of a width of the belt portion between the portions.