thermoforming and varnishing

[capiwalter]

First of all, excuse my very poor english!

Secondly I have a problem with a thermoforming of PC (1,5 mm of thickness) with a temperature of 165 C. After the thermoforming, in the varnishing, appears a lot of little bubbles in the surface of PC. When I varnish, in the same batch, pieces of injected PC this problem not occurs.

Are there some lights in the end of this hole?

Walter

[Louis]

How long after the thermoforming process or injection process is the Varnish applied? It sounds like moisture. The molding process will produce a very dry part, while the thermoforming process is a secondary process, so by nature, it will allow the PC to absorb some moisture.

Other that that, I can't think of anything else that might affect it.

Hope that helps!

[capiwalter]

We do the varnishing just after the thermoforming, without time to get moisture from the air. The strongest possibility appointed in our discussions is the migration to surface of the PC processing aid, forming little "pieces" of some stearate or another aid processing (I don't know what would be), and during the varnishing, these "pieces" avoid the total recovering of PC surface doing the "little-bubbles-impression".
We are thinking in two ways of solve the problem:

1. Because is possible to be a surface phenomena, we will try to do thermoforming with a level of some material above the PC to interact with the processing aid with the scope to not permit interaction between the aid processing and "spread" it. We tried this with a lubricant and worked well but the lubricant attacked the PC;

2. Some solvent to dissolve the aid processing. Somebody knows someone?

Excuse again my english errors!

My best regards

Walter