Manufacturing process to produce litho sheet

Abstract

The present invention provides an aluminum alloy for lithographic sheet including about 0.05 wt % to about 0.25 wt % Si; about 0.25 wt % to about 0.4 wt % Fe; less than or equal to about 0.04 wt % Cu; less than or equal to about 0.25 wt % Mn; 0.31 wt % to 0.35 wt % Mg; less than or equal to about 0.03 wt % Zn; less than or equal to about 0.03 wt % Ti; and incidental impurities. Another aspect of the invention is a method of processing a lithographic sheet including the steps of providing an aluminum sheet; contacting the aluminum sheet with an electrolyte bath; and applying a current having a non-sinusoidal wave form with a constant peak voltage to said electrolyte bath.

1 . An aluminum alloy comprising: 
 about 0.05 wt % to about 0.25 wt % Si;    about 0.25 wt % to about 0.4 wt % Fe;    less than or equal to about 0.04 wt % Cu;    less than or equal to about 0.25 wt % Mn;    0.31 wt % to about 0.40 wt % Mg;    less than or equal to about 0.03 wt % Zn; and    less than or equal to about 0.03 wt % Ti;    
   
   
       2 . The alloy of  claim 1  comprising Si ranging from about 0.8 wt % to about 0.12 wt %.  
   
   
       3 . The alloy of  claim 1  comprising Fe ranging from about 0.28 wt % to about 0.32 wt %.  
   
   
       4 . The alloy of  claim 1  comprising Zn ranging from 0.01 wt % to 0.03 wt %.  
   
   
       5 . The alloy of  claim 1  comprising Ti in less than or equal to about 0.014 wt %.  
   
   
       6 . The alloy of  claim 1  comprising Mg ranging from 0.31 wt % to about 0.35 wt. %.  
   
   
       7 . The alloy of  claim 1  comprising less than or equal to 0.007 wt % Cu.  
   
   
       8 . An aluminum alloy comprising: 
 about 0.8 wt % to about 0.12 wt % Si;    about 0.28 wt % to about 0.32 wt % Fe;    less than or equal to about 0.007 wt % Cu;    less than or equal to about 0.02 wt % Mn;    0.31 wt % to about 0.35 wt % Mg;    less than or equal to about 0.03 wt % Zn; and    less than or equal to about 0.014 wt % Ti;    
   
   
       9 . A method of producing a lithographic sheet comprising: 
 providing an aluminum sheet;    contacting the aluminum sheet with an electrolyte bath; and    applying a current having a non-sinusoidal wave form to said electrolyte bath at a constant peak voltage.    
   
   
       10 . The method of  claim 9  wherein the wave form of the non-sinusoidal current is either symmetrical or asymmetrical and is generated by a thyristor power supply to provide a desired current density to the aluminum sheet by moving the switching point of the thyristor power supply.  
   
   
       11 . The method of  claim 10  wherein the constant peak voltage ranges from about 35 to about 60 volts.  
   
   
       12 . The method of  claim 10  further comprising applying the non-sinusoidal wave form current with a current density ranging from about 4 to about 12 A/dm 2 .  
   
   
       13 . The method of  claim 12  comprising applying the non-sinusoidal wave form current for dwell times ranging from about 0.5 to about 3.0 seconds.  
   
   
       14 . The method of  claim 10  wherein the electrolyte bath comprises a mineral acid in a concentration of less than about 35%.  
   
   
       15 . The method of  claim 13  wherein the electrolyte bath comprises sulfuric, phosphoric, or sulfuric-phosphoric mixtures.  
   
   
       16 . The method of  claim 15  wherein the electrolyte bath comprises less than 20 g/l.  
   
   
       17 . The method of  claim 16  wherein the electrolyte bath comprises a temperature ranging from about 40° C. to about 100° C.  
   
   
       18 . The method of  claim 9  wherein providing the aluminum sheet comprises an alloy comprising: 
 about 0.05 wt % to about 0.25 wt % Si;    about 0.25 wt % to about 0.4 wt % Fe;    less than or equal to about 0.04 wt % Cu;    less than or equal to about 0.25 wt % Mn;    0.31 wt % to about 0.40 wt % Mg;    less than or equal to about 0.03 wt % Zn; and    less than or equal to about 0.03 wt % Ti;    
   
   
       19 . The method of  claim 18  further comprising using a thyristor power supply to generate the current having a non-sinusoidal wave form, wherein the power supply is configured to provide a current with a desired current density applied to the aluminum sheet by moving the switching point of the thyristor power supply.  
   
   
       20 . The method of  claim 19  wherein the electrolyte bath comprises sulphuric acid and then applying the pulse wave current comprises a current density ranging from about 4-12 A/dm 2  for dwell times of 0.5 to 3.0 seconds.