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Problems with lithographic plate anodizing

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Our company has a lithographic plate production line and the process is as follow:

1. electrograining;

2. desmut and rinse (at this point the plate looks white and without any lines)

3. anodizing;

4 D.I. water rinse; dry;

5. coat with the light sensitive coating; dry.

The problems are

1. the original lines can be seen again after anodizing.

2. the oxide layer cannot be any thicker otherwise the development will be impossible after exposure.

3. Since the line is designed sheet-fed, all the electrochemical processes cannot be made evenly; the electrograining produce a surface with coarser four corners and edges; however, the anodizing produce a surface with thicker oxide layer at the center. I suspect its the effect of current leakage for the anodizing while the opposite effect for the electrograining. As the anodizing bath's conductivity is much higher than the electrograining bath.

Any advice or consultant will be very welcomed.

wailok yee
- Hong kong

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I have never seen electrograining of aluminum, but agitation is important in most electrode processes. You may get a more even graining if you use high agitation, either through solution movement, air agitation, rocker agitation and the like. If your graining is an anodic process, make sure you keep the anode solution below the solubility of the reaction products over the entire surface. -tom

Tom Pullizzi Falls Township, Pennsylvania

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To Wailok Yee

It may be a little late but not to worry I'll bet you still have these problems or if not others. We specialise in troubleshooting especially on coil lines, but know and understand the sheet method. The process as you list it seems a little short of parts. Do you degrease/pre-etch and do you have a post anodising treatment? To help we would need to know more about the condition in your process eg current densities, types of acids and approx. concentrations. You may be walking a tightrope on specifications.

Ray Scott
- Leeds, UK

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Can litho plates be re-grained and resensitised and used a second time? How is it done?

Jagan Ridrich
- Mauritius