Aluminium lithographic sheet
View Patent ↗The invention relates to an aluminum alloy lithographic sheet product having an enhanced electrolytic graining response in which Zn between 0.5 and 2.5 wt % is added to an aluminum base alloy, in particular an alloy of the 1XXX, 3XXX or 5XXX series alloys. The invention also relates to a method of producing a lithographic sheet product.
1. A lithographic sheet comprising an alloy composition comprising 0.71-2.5% Zn wherein the alloy, apart from the Zn content, is an alloy from the 1XXX series of aluminum alloys.
2. The lithographic sheet of claim 1 wherein the lower Zn limit is 0.9%.
3. The lithographic sheet of claim 1 wherein the upper Zn limit is 2.0%.
4. The lithographic sheet of claim 1 wherein the upper Zn limit is 1.75%.
5. The lithographic sheet of claim 1 wherein the Zn content is 0.71-2.0%.
6. The lithographic sheet of claim 1 wherein the Zn content is 0.9-1.75%.
7. The lithographic sheet of claim 1 wherein the alloy, apart from the Zn content, is AA1050 or AA1050A.
8. The lithographic sheet of claim 1 wherein the alloy, apart from the Zn content, is in wt %; Mg 0.05 to 0.30; Mn 0.05 to 0.25; Fe 0.11 to 0.40; Si up to 0.25; Ti up to 0.03; B up to 0.01; Cu up to 0.01; and Cr up to 0.03; with unavoidable impurities up to 0.05 each and 0.15 total.
9. The lithographic sheet of claim 1 wherein the alloy, apart from the Zn content, is in wt %: Fe 0.30 to 0.40; Mg 0.10 to 0.30; Si 0.05 to 0.25; Mn up to 0.05; and Cu up to 0.04.
10. A method of producing a lithographic sheet comprising the following steps:
providing a sheet product with an electrograining surface of an aluminum alloy with a composition comprising from >0.5 to 2.5 wt % Zn wherein the alloy, apart from the Zn content, is an alloy from the 1XXX series of aluminum alloys; and
electrograining the surface in an acidic electrolyte with a total charge density ≦500 C/dm 2 .
11. The method of claim 10 wherein the total charge density used is ≦490 C/dm 2 .
12. The method of claim 11 wherein the total charge density is ≦450 C/dm 2 .
13. The method of claim 10 wherein the electrolyte comprises hydrochloric acid.
14. The method of claim 13 wherein the electrolyte comprises hydrochloric acid and sulphates.
15. The method of claim 10 wherein the electrolyte comprises nitric acid.
16. The method of claim 10 wherein the Zn content is 0.71-2.5%.