Polishing polycarbonate

Robin,

I remove scratches with Duraglit wadding silver polish. Take your time and work in small cicular motions and it will come out.

Mart> I tried cleaning one of the lenses on the new gauges on my kit car

suggest using 1200 grade wet & dry paper (used wet) first, in my experience it speeds up the process. old hairy face

I'll give the Duraglit a go first, because the surface isn't really scratched - it's been chemically eroded, so I think using 1200 W&D would actually make things worse...

...that said, if the Duraglit doesn't work, then I'll give the sandpaper a go - perhaps I'll have trendy "frosted glass" dials - I'll have to treat all of them then so they match!!

In article , Robin writes

I'll X-post this to a man who should know.

Cane! You there?

Polycarbonate, whilst being a wonderfully impact resistant material is very chemically pathetic. It is unfortunately attacked by many common household chemicals let alone industrial grade solvents unless it has been hard-coated with polysiloxane. You may well find that you will experience further degradation of the dial covers and possible stress cracking. Thats the bad news.

Depending on just how badly the surface is eroded is you may need to go through a few steps to clean it up, by first removing the coarser erosion then going finer on polishes to remove the previous set of scratches. I'm not sure what is in the Duraglit, but it may not be a bad choice at all if the original pits aren't too deep. When you need to go finer than the Duraglit can manage you might want to consider Jewellers Rouge.

Just remember to pretty much avoid all chemicals. A mild washing-up liquid solution is going to be fine, but dont use anything with strong alcholhols, esters, or alkalis.

Peter

Avoid

Bad form I know, replying to my own post, but I just found this site which may have just what you're looking for.

Peter

I'm here.

There's not much point in trying to polish polycarbonate once it's reached this stage. This is an ex lens, it has ceased to be.

Polycarbonate is specified because of it's impact resistance and good fire rating. Unfortunately it's surface is soft and very susceptible to abrasion even when you think you're being gentle.

The following link is for information on a brand of polycarbonate sheet called Makrolon. Too much information really but it may be of use in the future.

If you're able to machine a new lens from flat sheet let me know and I'll post you a couple of off cuts to play with.

Are you sure it's not just resting?

Umm, correct me if I'm wrong, but ISTR that all modern CDs (the music kind) are in fact, polycarbonate. Therefore, any polishing method that works on them, might also work on the problem?

YMMV, obviously. But if it's completely stuffed anyway, why not look up some of the "My CD won't play as it's scratched" fixing tips in abundance on the interwebs?

-- Nath

Nearly right. CDs are injection moulded and then have a clear varnish applied to the surface to reduce scratching.

If you're really determined to polish polycarbonate car polish like Turtle Wax sometimes works but it's not guaranteed.

Link of interest : more than you ever wanted to know about CD manufacture.

-- Nath

Yes and No:) The CD's are made from Polycarb but then they are spin coated with Polysiloxane lacquer which is UV cured to harden it. I've always been a bit dubious about how these kits can repair the CD as the scratch is usually deep enough to damage the sputtered aluminium coating underneath.

As this is usually only angstrom units thick its easy to damage. The lacquer coating is usually somewhere in the order of 30 microns thick and I'm sure that all these kits do is fill in the gaps here and smooth off nasty angles raised by the scratch which could affect the refraction from the aluminium.

However, getting back to the gist of it, its definitely worth a try. As the PS lacquer coating (depending on thickness) can be hard enough to resist rubbing with wire wool, anything that works to polish this will polish/remove material from uncoated Polycarbonate much easier.

On a similar note, the lens covers could have been made from Acrylic rather than Polycarbonate which has a slightly harder surface and is more amenable to polishing. If I could hold a match to it and sniff the fumes I could tell you, but then again this would only damage it further so forget that (doh!) and I haven't got a smellyvision plug-in on my PC yet.

Peter

A CD has two sides, the top and the bottom. Assuming the CD starts as a 2 mm thick layer of polycarbonate, the metallisation is on top, and this is alwways protected by a further layer of plastic, usually acrylic.

The bottom is usually coated, but sometimes not. In either case polishing the bottom will not affect the aluminised layer until you have polished away all 2 mm of the polycarbonate, which will take you much longer that you want to spend doing it :)

Toothpaste works reasonably okay, though cerium oxide is better for a good final finish. You need _lots_ of elbow grease! To get it to polishable condition you can use green scouring pads - some white ones will work too, but not all.

Another option is to coat the piece with a transparent plastic - I have no experience with this at the hobby/home/amateur level, though I could make some suggestions - and polish that.

BTW You want to polish a CD so the direction of polishing is away from the centre, or at 45 degrees at most. The error-correcting mechanisms of the CD system do not work very well with scratches parallel to the track, but they work wonders with scratches at right angles to it. (only one track, like an LP has two)

Peter, you're right of course, that I got it completely wrong by implying that the metallising is on the bottom when it is in fact as you've stated on the top. And right again in that polishing through

1.2mm of polycarbonate would be rather tiresome:) I won't tell you how embarassed I am to make that error in print after running a similar business for 3 years...... However, all that is on top of this is the PS lacquer coating, and often a screen printed layer on some commercial content discs. There is definitely no other protection applied over the top of this though. Regards

Peter

I love it when you talk dirty.

I think I'll try damaging an old CD with acetone and then polishing it again...