Alcan International Limited

Novelis, Inc.

Jonathan Ball

Martin Philip Amor

Peter Karl Limbach

Nigel C Davies

John A Hunter

John Andrew Ward

John A Treverton

Eric Barlow

Peter R Andrews

John A Ward

Rodney Charles Jones

Armin Kumpart

Peter Karl Ferdinand Limbach

There is disclosed a process for producing an aluminium alloy sheet, which comprises subjecting a surface of the sheet to anodising conditions to form on the surface an aluminium oxide barrier layer of thickness 10 to 50 nm and treating the oxide layer with an aqueous solution of alkali to remove the layer, thereby leaving a roughened surface on the alloy sheet.

Aluminium alloy sheet with roughened surface

Aluminium sheet suitable for use as a lithographic plate support has a surface that is uniformly rough by virtue of: a rippled topography having an aspect ratio of at least 1.3 on a sale of 5-200 &mgr;m; and a superimposed pitted structure on a scale of 1-20 &mgr;m. A method of making the aluminium sheet involves pack rolling two aluminium ribbons to generate facing surfaces having the transverse rippled structure; followed by a small amount of a conventional roughening or graining treatment to develop the pitted structure.

Aluminium sheet with rough surface

An aluminum workpiece, e.g. sheet for containerstock, having an anodic oxide film whose thickness varies from location to location on the surface, whereby interference contrast effects are visible on the surface. Aluminum foil having on a surface thereof an unsealed anodic oxide film 5-1000 nm thick which provides a clean surface with fretting resistance. A method of anodizing thin aluminum foil is also described.

Aluminium workpiece

Surface defects on rolled alulminium alloy sheet, particularly that intended for use as lithographic plate substrate, are caused by copper-containing particles. The invention provides a method of improving the sheet by removing the particles by anodising in an aggressive electrolyte, particularly a.c. anodising at a current density of at least 2 kAm,.

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Deddington, United Kingdom

Jonathan Ball