Printing HDPE onto copper

Copper is a world champion for conducting heat. Of course when you try to put molten plastic on it, especially a tiny little track of CAPA on it it can be expected to instantly chill and likely not make a good bond with the copper.

Vik mentioned that he'd cleaned the surface of the copper before trying to print. That was something I hadn't done, so I set out to repeat my attempt to HDPE on copper in Tommelise. This time, however, I thoroughly cleaned the copper surface with vinegar and then rinsed it off and dried it with a clean cloth.

I had set the copper sheet onto Tommelise's xy worktable and was preparing to try to print on it when I something hit me that both Vik and I had missed.

The copper needed to be warm so that the HDPE would have a chance to bind to the surface. I got out my hot air paint stripper, my IR thermometer and went into the kitchen. I put the copper on one of the electric heating elements on my stove. I then realised that it was going to take quite some time to heat that big a piece of copper with a paint stripper.

Why not just turn the stove heating element under the copper on?

I did that and then monitored the temperature of the copper till it was about 10-20 degrees above the melting point of HDPE according to my IR thermometer. At that point I put a 50 mm length of 3 mm HDPE filament onto the copper surface and then heated it with the paint stripper.

The HDPE went transparent almost instantly.

I continued to play the hot air over the HDPE waiting for it to slump a bit so that I would have a good contact surface on the copper. Then something entirely unexpected happened.

In the blink of an eye the 50 mm piece of HDPE filament contracted to 15 mm. When I say, blink of an eye, I'd say that the sudden contraction happened in about 0.1-0.2 seconds. It was almost instantaneous. I was so startled that I nearly dropped the paint stripper.

After a while the chunky little cylinder of HDPE slumped a little bit so I turned off the paint stripper and turned down the stove element to let things cool slowly.

At that point it occurred to me that I might as well try CAPA, too. When the copper temperature got down to about 80 I put a 50 mm piece of CAPA onto the copper and played the paint stripper air stream on that, too. The CAPA slumped instantly so I cut the heat off and let things cool down.

I then took the copper sheet and put it on a Corelle Ware (very heat resistant) plate and photographed it.


Here you can see that the HDPE on the upper half of the copper sheet has chilled while the CAPA is still transparent.

After the plate was back to room temperature I found that the HDPE had formed quite a strong bond with the copper. The CAPA had not and peeled off rather readily. I can't get the HDPE off with my fingers even though the contact surface between copper and HDPE only amounts to maybe 10 mm^2.

I'm not satisfied that CAPA can not be made to bind to copper. This first experiment didn't demonstrate that it would, but I tried to melt it onto the copper plate only as an afterthought. Somebody in the RepRap team who is more interested in using CAPA than I am ought to repeat the experiment with CAPA to confirm or disprove my slapdash experiment. It would be very important for RepRap if CAPA could be bound to copper.

HDPE, on the other hand, can.

The problem is that that is of no particular use to anybody wanting to do photoresist etching on a prepared PCB. It is, however, very much of use to somebody wanting to make up PCB boards out of copper foil and HDPE.

Put a small hot plate on Tommelise's xy worktable and you're good to go.