Method for producing an aluminum foil with integrated security features

Abstract

Method for producing an aluminum foil with integrated security features. An aluminum foil is rolled to a thickness of less than 150 μm in multiple cold rolling passes, and simultaneously a texture which runs in the rolling direction is produced on both faces of the foil. A loose composite formed from at least two of the aluminum foils, is fed into a pair of working rollers in a final cold rolling pass, wherein the relief-like surface structure which is produced in the rolling direction via a polishing process has been reduced by 10 to 50% with respect to the average roughness height in one region in a contrast- and motif-dependent manner on at least one roller surface in order to form a motif for a security feature. The security feature is transferred onto the aluminum foil face facing the roller surface, and the loose composite of aluminum foils is separated.

1 . Process for the manufacture of an aluminum foil ( 1 ) with integrated security features ( 6 ) whereby an aluminum foil ( 4 ) is rolled in several cold rolling passes to a thickness of less than 150 μm, and whereby at the same time on outer faces ( 4   a ,  4   b ) of the aluminum foil a texturing ( 5   a ,  5   b ) extending in rolling direction is created, whereby a loose composite ( 8 ) is formed from at least two of those aluminum foils ( 4 ) which composite is fed into a working roller pair ( 9 ) in a last cold rolling pass, in which on at least one roller surface ( 11 ) the relief type surface structure produced by grinding is reduced, depending on contrast and motif in a range ( 6 ′) of 10-50% relative to the average depth of roughness, for the formation of a motif for a security feature ( 6 ) which is transferred to the outer face ( 2   a ) of the aluminum foil facing the roller surface, whereafter the loose composite ( 8 ) of the aluminum foil ( 1 ,  4 ′) is separated. 
     
     
         2 . Process according to  claim 1 , characterized in that the last cold rolling pass is carried out with a closed roller gap ( 9 ′) and a defined mixed friction range is adjusted according to the Stribeck curve by way of the parameters friction co-efficient, dynamic viscosity of the rolling oil, rolling speed and rolling pressure and at the same time longitudinal tension is applied in the closed roller gap ( 9 ′) to the aluminum foil ( 4 ) which acts against the shape change resistance of the aluminum foils. 
     
     
         3 . Process according to  claim 1 , characterized in that for the last cold rolling pass on the roller surface ( 11 ) the relief type surface structuring ( 11   a ) produced in rolling direction is reduced in its average depth of roughness by way of laser beams. 
     
     
         4 . Process according to  claim 1 , characterized in that in the aluminum foils ( 4 ) used, no undesired strikethrough of the motif ( 6 ′) for the security feature ( 6 ) on to the other outer face ( 2   b ) of the aluminum foil ( 1 ) occurs, due to providing a release agent ( 7 ). 
     
     
         5 . Process according to  claim 1 , characterized in that because of the tribologic conditions in the closed roller gap ( 9 ′) the physical and/or chemical properties of the aluminum foils ( 4 ) are maintained even in the end product ( 1 ) of the process. 
     
     
         6 . Aluminum foil ( 1 ) with integrated security features ( 6 ) manufactured with the process according to  claim 1 , characterized in that the security features ( 6 ) are present in an amount of at most  30 % per unit of surface. 
     
     
         7 . Aluminum foil according to  claim 6 , characterized in that the security features ( 6 ) are present in the form of letters, fantasy signs or lines. 
     
     
         8 . Aluminum foil according to  claim 5 , characterized in that the security features ( 6 ) can only be removed by destruction of the foil surface. 
     
     
         9 . Aluminum foil according to  claim 5 , characterized in that the aluminum foil ( 1 ) is not subject to a shape change in the region of the first, second or third order after the last cold rolling pass. 
     
     
         10 . Aluminum foil according to  claim 5 , characterized in that the region of the security feature ( 6 ) appears dull, whereby the surface ( 2   a ) appears glossy because of the directed texturing ( 3 ). 
     
     
         11 . Process according to  claim 2 , characterized in that for the last cold rolling pass on the roller surface ( 11 ) the relief type surface structuring ( 11   a ) produced in rolling direction is reduced in its average depth of roughness by way of laser beams.