Stefan Trethan wrote:
> On Fri, 15 Sep 2006 21:15:59 +0200, derekhawkins <eldata@...> wrote:
>
>
>>Either can be formulated to block UV.
>
>
> I think it is more like PMMA can be made to block UV (for example with
> special coatings).
> I don't think polycarbonate can be made to allow UV to pass.
> Again, not 100% sure.
>
> ST
>
>
Not sure about polycarbonate, but when I used 2mm PMMA sheeting ("non UV
blocking" type) for my first light box it took about twice as long to
expose photoresist than it did after changing to standard 3mm window
glass. There is nothing wrong with common window soda glass.
I know that the coated 0.20mm polyster films used for inkjet
transparencies, also contribute significant UV absorbtion. It was a
while since I did the test, but from memory the film almost doubled the
exposure time. Of course there is no way to get around this problem.
Conclusion: avoid PMMA if possible.
Adam