DE2149899A1 - Process for producing an even and fine roughening on aluminum surfaces - Google Patents

Description

SWISS ALUMINUM AG, CHIPPIS

Process for producing a uniform and fine Roughening on aluminum surfaces

Priority: Oct 6 197o; Switzerland; No. 14827 / 7o There are different procedures and bath composition ^! known for chemical and electrolytic etching of aluminum surfaces. However, these do not meet the requirements that on decorative surfaces and above all on the roughening of lithographic sheets and offset foils (flat printing forms) will. For this purpose, the surface must be evenly and finely roughened. In the etching of Electrode foils for electrolytic capacitors require the greatest possible surface enlargement. The achieved Roughness depths are probably considerable but different at the individual etching attack points. For the above purposes however, a uniform surface roughness is required, whereby the extent of the surface enlargement does not play a role. In many electrolytes, the throwing power is also insufficient to achieve a constant roughening over the whole Surface.

Our investigations have shown that the known processes can be improved if the salt or salt

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pitric acid to existing electrolytes boric acid and with Alternating current is etched at low current densities.

The invention accordingly relates to a method for producing a uniform and fine roughening on aluminum surfaces by electrolytic etching in a bath containing hydrochloric acid and / or nitric acid and its use for producing flat printing forms made of aluminum. The method is characterized in that the Aefczung with alternating current in an aqueous solution of 0.5-2 wt. 0.5-5 wt.% Of nitric acid and 0.1-1.5 Gevi.% Boric acid, BEZW. a corresponding amount of a borate, at room temperature and a current density of 0.5-10, preferably

3-5 * A / dm is carried out.

This process results in even and finely roughened surfaces, the high demands with regard to the decorative appearance and the use as lithography sheet and offset foil are sufficient. The fourth advantage here is that you can work at room temperature and that the result is achieved if this is adhered to a minimum treatment time does not depend on the further treatment time. The current density is significantly lower than it is commonly used in the roughening of electrode foils for electrolytic capacitors.

Example:.. A Ileinaluminiumblech was contains an electrolyte containing 1.5 wt $ hydrochloric acid and 1.0 wt% of boric acid, currency.

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_^ 2ΊΑ9899

rend five minutes nit alternating current (50 Hz) at room temperature and a current density of * ί A / dm '"treated" The roughening achieved was very evenly with a roughness of _<)} .2 \ in _t same' results were obtained when instead of hydrochloric acid, 2.5% by weight of nitric acid were used.

Higher concentrations, namely over 2% hydrochloric acid respectively. over 1% nitric acid and 2% or more boric acid resulted in an irregular, coarse surface enlargement which cannot be used for decorative purposes ^ and is also not suitable for planographic printing forms. In the same way, a current density of over 10 A / dm has an unfavorable effect.

The surfaces roughened after the process can be after known processes are anodically oxidized to maintain a clean appearance in decorative applications or in the production of lithographic sheets and offset printing foils. The process is particularly suitable for the production of planographic printing plates suitable to be photosensitive before overcoating Layers are anodically oxidized, since the fine roughening has a high contour definition even after the anodic oxidation of the printed picture guaranteed. For this application the etched Plate or film is anodically oxidized by known methods and then coated with the photosensitive layer. During the development of the exposed plate, the oxide layer is removed from the non-printing areas, while the areas left with the oxide layer form the printing areas.

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Claims (4)

Claims 1.) Method of producing a uniform and fine Roughening of aluminum surfaces through electrolytic etching in a bath containing hydrochloric acid and / or nitric acid, thereby characterized that the etching with alternating current in an aqueous solution of 0.5-2% by weight hydrochloric acid bzv /. o, 5-3 wt.% nitric acid and o, l-l, 5 wt.% boric acid, or a corresponding. Lc-uge of a borate, at room temperature and a current density of 0.5-lo A / dm is carried out. 2. The method according to claim 1, characterized in that the etching is carried out with a current density of 3-5 A / dm ² . 3. The method according to claim 1 or 2, characterized in that it is made for the production of planographic printing plates Aluminum is used. 4. The method according to claim 3, characterized in that the Plachdruckformen prior to coating with _photo-: are oxidized anodically sensitive layers. 209816/1397