Better living through chemistry (get your geek on)

[Janeiac]

Surfing the web, I found details of patents to chemically smooth and shape various types of plastic.
Probably the experts on this forum know all about it.

I thought perhaps someone on here would be able to put it into plain English to help in  restoring old phones. If we could find an agent that reflows the surface, it could possibly be used to repair small cracks or dings. I have an early 500 with two melted spots (looks like a careless cigarette or soldering iron) that would be a candidate to experiment on. I do have a light and deft touch for this sort of thing.
Any ideas on how to extract the pertinent info?

Going to one page brings up a list of related patents. A geek could spend a lot of time clicking on links. I'm not admitting to spending hours reading, I'm just saying. <grin>

http://www.google.com/patents/US3437727
"The surfaces of a cellulose acetate butyrate or a cellulose propionate plastic article are refinished by applying thereon a solvent which removes any outer, deteriorated layers of plastic, exposes new surfaces, and dissolves a portion of the newly exposed surfaces. "

[TelePlay]

Here's one topic that is similar. It has a few links to other topics.

http://www.classicrotaryphones.com/forum/index.php?topic=5260.0

I'll look for more.

[TelePlay]

This is the one I was thinking about.

http://www.classicrotaryphones.com/forum/index.php?topic=5030.msg62854#msg62854

[Janeiac]

Neat-o-- Thanks!

[Janeiac]

I found this:
http://www.google.com/patents/US2651811

The chemist says a roughly 50-50 mix of isopropyl alcohol and toluene or xylene can re-melt certain plastics that are dipped and briefly soaked. Anyone try it?

[JorgeAmely]

Search for Chuck Hensley here in this forum. I believe he experimented extensively on this topic.

[Janeiac]

Thanks for the tip... I did find his posts and tech docs, but nothing on that particular subject.

[unbeldi]

The idea of solvent polishing, "reflowing the surface", etc., may seem attractive after considering—well, especially after having done it a few times—the alternatives of mechanical labor in sanding a surface with ever higher grit of paper or polishing cloth.

However, as easy as it sounds often when reading the many patents and recipes on the subject, it requires a lot more skill, patience, equipment and patience to perfect. Sometimes the initial results seem astonishing when one gets lucky and it can indeed be a time saver.

However, overall, I have yet to find the consistency in the process that I would desire, and I have had always to resort to polishing at least parts of the surface that I treated.

Every plastic surface, or bulk for that matter, has internal material stress built up, especially decades-old plastic parts that had seen exposure to the environment. Most often such stress is relieved as soon as the material has an opportunity, such as when applying a solvent to the surface, or heat.  Some surfaces develop crazing without external help.

I have observed that after solvent exposure, plastics had tiny wrinkles on the surface.  Sometimes this can be corrected with more solvent, but in the end I have always had to mechanically polish the surface nevertheless, albeit with much higher grit than otherwise. So it still was a saving in time.

In order to this correctly and successfully in repetition, the conditions have to be well stabilized and controlled in a closed chamber.

The methods that suggest using solvents with low vapor pressure (higher boiling point) such as toluene and xylene mixtures, take advantage of the rather low solubility of, say, cellulose acetate (Tenite, CAB) in them, in contrast to solvents like the ketones (acetone, MEK) or esters.  This takes more time, but the items need to be completely immersed into the solvent for some time (minutes), not merely seconds, and take much longer to dry. This requires an enclosure to control dust.

If you want to embark on these methods, it takes personal research, effort, and patience. You still need the old techniques to correct mistakes and failures.

[Janeiac]

Thanks so much for sharing your observations. I was interested to hear from someone who tried this. I had assumed to do this correctly one would need industrial equipment such as a booth or chamber and wasn't going to go attempt anything like it.

I did some searching and found a YouTube video by someone who had used this method on a car hood-- I think he had done a restoration using some type of plastic or fiberglass. He wasn't happy with the uneven surface and was trying to correct it with a handheld sprayer application of toluene. It worked quite well, and obviated the necessity of multitudinous hours of sanding.

I thought  I might try a small paintbrush direct application on one particular melted spot on this one phone I have and then try to smooth it with a flat spackling blade. It looks like someone accidentally touched it with a soldering iron, or perhaps a lit cigarette. Does that sound feasible?

[unbeldi]

Thanks so much for sharing your observations. I was interested to hear from someone who tried this. I had assumed to do this correctly one would need industrial equipment such as a booth or chamber and wasn't going to go attempt anything like it.

I did some searching and found a YouTube video by someone who had used this method on a car hood-- I think he had done a restoration using some type of plastic or fiberglass. He wasn't happy with the uneven surface and was trying to correct it with a handheld sprayer application of toluene. It worked quite well, and obviated the necessity of multitudinous hours of sanding.

I thought  I might try a small paintbrush direct application on one particular melted spot on this one phone I have and then try to smooth it with a flat spackling blade. It looks like someone accidentally touched it with a soldering iron, or perhaps a lit cigarette. Does that sound feasible?

Once you exposed the surface to solvent, you must not touch it with anything. You just cannot get it smooth with a tool. Other than leaving marks, it may actually stick to the tool and draw thinner-than-hair threads.

I have fixed burn marks by sanding them down to achieve smoothness on the edges, and then I have filled in the crater with dissolved plastic solution, one drop at a time to build up bulk above the edge for final sanding.

But by all means, try out any technique you think might help. Experience is invaluable. There are plenty of old broken phones around for practicing. Here is a phone that I partially solvent polished with special polish cloth soaked in acetone/ethyl lactate mixtures.  The phone had a serious crack in the front corner up the face next to the dial. The thread for this phone is here: http://www.classicrotaryphones.com/forum/index.php?topic=11993.0 I have also used acetone sprays, repurposing spray bottles from certain medications, that produce a very fine mist.  I don't think I have pics of that.

[cihensley@aol.com]

My experience with the various chemical processes pretty much matches the multiple posting by unbeldi.

Chuck

[HarrySmith]

Here is Chuck's thread from 2011: http://www.classicrotaryphones.com/forum/index.php?topic=5260.15

[Janeiac]

Thanks very much, everyone, for pointing me to the threads and for sharing the information and pictures. I really appreciate the extra time you took to post it. It's really fascinating.

The pictures are great! everyone did a wonderful job and I am truly grateful for your sharing. I LOVE the way the colored phones turned out. It's good on so many levels, from saving old phones to keeping garbage out of landfills.