Adhesive tape

Abstract

An adhesive tape wherein the backing film comprises at least two coextruded layers of different composition, whose interface is not planar but instead has a nonlinear course in cross section, which continues laminarly in the machine direction, has been oriented in the machine direction, and has plane-parallel outer faces.

What is claimed is:  
     
         1 . An adhesive tape wherein the backing film 
 has at least two coextruded layers of different composition, whose interface is not planar but instead has a nonlinear course in cross section, which continues laminarly in the machine direction,    has been oriented in the machine direction, and    has plane-parallel outer faces.    
     
     
         2 . A film as set forth in  claim 1 .  
     
     
         3 . A process for producing a film or adhesive tape, comprising the following operations: 
 melting at least two materials of different composition in extruders    combining the melt streams in a die which by virtue of its construction leads to a non-planar interface as set forth in  claim 1     cooling the melt to a film    orienting the film in the machine direction.    
     
     
         4 . The adhesive tape as claimed in  claim 1 , wherein the backing film in the machine direction has a residual strength of at least 50 N.  
     
     
         5 . The adhesive tape as claimed in  claim 1 , wherein the backing film in the machine direction has a residual strength of at least 100 N.  
     
     
         6 . The adhesive tape as claimed in  claim 1 , wherein the backing film in the machine direction has a tensile strength of at least 200 N/mm 2 .  
     
     
         7 . The adhesive tape as claimed in  claim 1 , wherein the backing film in the machine direction has a stress at 10% elongation of at least 100 N/mm 2 .  
     
     
         8 . The adhesive tape as claimed in  claim 1 , wherein the backing film has a cross-direction tensile impact strength of at least 50 mJ/mm 2 .  
     
     
         9 . The adhesive tape as claimed in  claim 1 , wherein the backing film has a cross-direction tensile impact strength of at least 100 mJ/mm 2 .  
     
     
         10 . The adhesive tape as claimed in  claim 1 , wherein the cross-directional tensile impact strengths of two intermeshed layers in the oriented state differ by a factor of at least two.  
     
     
         11 . The adhesive tape as claimed in  claim 1 , wherein the difference in thickness within a layer of two intermeshed layers of the backing film is more than 10%.  
     
     
         12 . The adhesive tape as claimed in  claim 1 , wherein the difference in thickness within a layer of two intermeshed layers of the backing film is more than 20%.  
     
     
         13 . The adhesive tape as claimed in  claim 1 , wherein the number of thickness maxima and, respectively, minima in the cross-direction within a layer of two intermeshed layers of the backing film is at least 3 per cm width.  
     
     
         14 . The adhesive tape as claimed in  claim 1 , wherein the number of intermeshed interfaces of the backing film is greater than one.  
     
     
         15 . The adhesive tape as claimed in  claim 1 , wherein the backing film has two intermeshed layers and one further smooth (non-intermeshed) layer.  
     
     
         16 . The adhesive tape as claimed in  claim 1 , wherein the backing film comprises polymeric raw materials having melt indices of 0.3 to 15 g/10 min.  
     
     
         17 . The adhesive tape as claimed in  claim 1 , wherein the backing film comprises polystyrene in one of the intermeshed layers and polypropylene in the other intermeshed layer.  
     
     
         18 . The adhesive tape as claimed in  claim 1 , wherein the backing film comprises more polystyrene than polypropylene in one of the intermeshed layers and more polypropylene than polystyrene in the other intermeshed layer.  
     
     
         19 . The adhesive tape as claimed in  claim 1 , wherein the thickness of the backing film is from 50 to 90 μm.  
     
     
         20 . The adhesive tape as claimed in  claim 1 , wherein the backing film has been oriented with a draw ratio of from 1:5 to 1:10.  
     
     
         21 . The adhesive tape as claimed in  claim 1 , wherein the backing film has two intermeshed layers and one further non-intermeshed layer, the middle layer having a lower cross-direction tensile impact strength than the outer layers.