Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: freedda on 07/03/2008 15:55:31
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I'm new to this forum, but read another thread about which colors block UV light. The responders seemed to agree that, just based on the color of a material, you couldn't say which color would be best at blocking UV light.
My question and use are a bit more specific: I'm printing transparencies on my Epson inkjet printer which I'll then use to expose light-sensitive plates in a UV exposure unit. I'm trying to find out which inks, besides black, would be best a blocking UV light.
There was a discussion on another thread that seemed to reason that the best ink colors were those that were furthest away from the UV end of the spectrum, but I'm starting to think that this might not always hold true.
Any info. or thoughts on this would be appreciated. Thanks, David.
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The cheapest black pigmment is carbon. This will block UV.
If you really need one that isn't black, try yellow. If you need a real answer then I'm afraid you need soemone with a spectrometer.
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...I'm printing transparencies on my Epson inkjet printer which I'll then use to expose light-sensitive plates in a UV exposure unit. I'm trying to find out which inks, besides black, would be best a blocking UV light.
Hi David,
If you're trying to make a UV exposure-mask (much like you do when making a printed circuit board at home), then I'd have thought you're much better off using a laser printer (you must use special high-temperature transparency film, as sold specifically for laser-printing or photocopying - the normal stuff will melt inside the printer).
The laser printer uses carbon-based toner, which is opaque to IR, visible and UV. Depending on the blackness of your print, if you time the UV exposure carefully, you should get away with a single print - but if you want more leeway in your exposure then printing the mask twice and carefully overlaying the two transparencies will give you even greater density. Arrange your mask so that the toner-side of the transparency rests against the UV-sensitive layer, as this will give better-defined edges.
I'm never tried making UV masks with inkjet, but to be honest I can't see it working. I'd have thought all inkjet inks will use dyes rather than pigments (particles) since the pigments would be expected to block the microscopic ink-jets.
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Could someone let me know what wavelength UV we are talking about here? There's a potential problem if the "clear" bits of the overhead slide film absorb too much UV. On the other hand there's nothing to say the UV has to be blocked by a pigment like carbon black. A dye would work perfectly well; if it looks black it probably blocks UV too.
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Could someone let me know what wavelength UV we are talking about here? There's a potential problem if the "clear" bits of the overhead slide film absorb too much UV. On the other hand there's nothing to say the UV has to be blocked by a pigment like carbon black. A dye would work perfectly well; if it looks black it probably blocks UV too.
Obviously I can't speak for the original poster, but for PCB-making we're talking 365nm (and maybe some 302nm) wavelengths from a mercury tube.
The thinnest of layers of all plastics I've tried completely block 254nm (I needed to arrange 254nm exposures of storage-phosphor screens for one aspect of my PhD). You need pretty esoteric (read expensive) materials if you want to pass 254nm!
UV-exposure boxes for small-scale simple PCB-making typically have a 4mm thick piece of glass or perspex through which the light passess.
For PCB photo-resist, you can get away with sunlight exposure, but of course the required exposure-time is highly dependent on time of day, time of year, location, cloud, etc etc, and is therefore hard to judge. I have successfully used a cassette- or CD case to press the mask flat against the board...
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If there's a "next time" try using polethylene or polypropylene. If they are free from additives they should pass 254nm UV fine. PMMA should just about manage it (but often won't due to additives or leftover monomer).
formaplas.easymax.net/pics/File/PMMA%20fiche%20technique.pdf
shows that it can transmit UV.
Anything with any benzene type rings in it (PET, polycarbonate polystyrene) will block short UV and possibly long wave UV too.
To get back to the original question, I'd go for black or yellow.
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Hi David.
I have had some experience with printing masks on an inkjet printer that have been successfully used for printed circuit work.
These were then exposed using a 15w compact fluorescent Blacklight lamp.
The main thing is to use the correct acetate transparency as you can get printable acetate sheets that are designed for an inkjet. They have a special coating on one side that gets printed on.
The first time I tried it didn't work too well as the print was not dark enough. I then changed the print setting to black and high quality and printed it out, then let it dry and printed it again. That was better, produced some usable boards but not 100% perfect.
The printed side of the mask must also be next to the plate to stop any light bleed.
Because of the hassle printing the next time I will try and use a laser printer as I'm told that is much more reliable.
Hope that may help.