EP0466644B1 - Process for roughening the surface of an aluminium strip - Google Patents

Description

The invention relates to a method for producing a strip from aluminum or an aluminum alloy with a roughened surface for lithographic printing plates, the strip being produced from a roll bar by hot and / or cold rolling.

• Eine gleichmässige Oberfläche, die sich gut zur mechanischen, chemischen und elektrochemischen Aufrauhung eignet.
• Eine harte Oberfläche nach dem Anodisieren, was eine grosse Zahl von Abdrucken ermöglicht.
• Leichtes Gewicht.
• Niedrige Gestehungskosten.

Lithographic printing plates made of aluminum, which are typically about 0.3 mm thick, have advantages over plates made of other materials, only a few of which are mentioned here:

• A uniform surface that is well suited for mechanical, chemical and electrochemical roughening.
• A hard surface after anodizing, which enables a large number of impressions.
• Lightweight.
• Low production costs.

ALUMINUM ALLOYS AS SUBSTRATES FOR LITHOGRAPHIC PLATES by F. Wehner and R.J. Dean, 8th International Light Metal Conference Leoben-Vienna 1987, gives an overview of the production and properties of tapes for lithographic printing plates.

In the conventional production of aluminum strip for the production of printing plates, the strip has an anisotropic surface topography as a result of the roll grinding and thus the directional structure of the roll surface as well as the practically uniaxial deformation of the material in the roll gap. In further steps the rolled strip is pickled, then roughened to the desired roughness mechanically, chemically or electrochemically or in a combination of these processes and, if necessary, anodized.

In view of these circumstances, the inventor has set itself the goal of providing a method of the type mentioned at the outset which, without an additional work step, requires the setting of an isotropic, i.e. structure of the strip surface with a high degree of roughness, independent of the rolling direction.

In order to achieve the object according to the invention, the last roll pass is carried out with a roll machined in accordance with the desired surface topography and roughness of the strip with a small pass decrease.

In extreme cases, the stitch decrease can be practically zero, i.e. the last roll pass would thus correspond to a pure stamping process. For reasons of economy, however, it is expedient to carry out a pass reduction in the course of the entire rolling process, the pass reduction being a maximum of 50%.

In the conventional production of aluminum strip, the rollers are provided with a roller cut, the rollers following in the direction of the strip run having an ever finer cut. In a further embodiment of the method according to the invention, it can now be provided that the penultimate roll pass is carried out with a roller with a coarse roller cut, contrary to the customary practice. The distribution of the rolling oil on the strip surface and subsequently the processes in the roll gap of the last roll are influenced in a favorable manner in such a way that the stitch reduction with the last roll can be relatively large, without the quality of the surface topography to reduce the roughness of the final rolled strip.

The processing of the surface of the roll used according to the invention for the last roll pass can be carried out in a known manner by blasting, e.g. Steel shot peening, spark erosion, laser texturing, electron beam texturing, chemical and / or electrochemical roughening or other roughening processes take place. The choice of processing method depends on the type of roughness pattern desired and the degree of roughness, i.e. the roughness depth, the average distance between the roughness peaks and other parameters.

The roughening of the strip surface influences the subsequent pickling and etching steps on the way to the production of the lithographic printing plates, leads, among other things, to a faster and more uniform attack of the pickling and etching solutions and can also enable the setting of different surface topographies. With the method according to the invention it is also possible to apply a roughness pattern to the surface of the strip during the rolling process during the production of the strip, which pattern already largely corresponds to the roughness pattern desired on the lithographic printing plate.

Claims (5)

1. Process for producing a strip of aluminium or an aluminium alloy with a roughened surface for lithographic printing plates, in which the strip is manufactured by hot and/or cold rolling from a rolling slab, characterised in that the last roll pass is effected by a roll with a low pass reduction machined in accordance with the desired surface topography and roughness of the strip.
2. Process according to claim 1, characterised in that the penultimate roll pass is effected by a roll with a rough roll polish.
3. Process according to claim 1 or claim 2, characterised in that the last roll pass is effected with a pass reduction of a maximum of 50 %.
4. Process according to claim 3, characterised in that the last roll pass is effected as a stamping pass.
5. Process according to one of claims 1 to 4, characterised in that the surface of the roll provided for the last roll pass is machined by blasting, spark erosion, laser or electron beam texturing or by chemical and/or electrochemical roughening.