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Plating a plastic Van de Graaff generator

2007

Hi

I am an engineer working for a electroplating company and we are trying to do electroless nickel plating on plastics rather cheaply because a customer asked us if we could do it. I have read on the forum various ways to plate plastics like stannous chloride and then palladium chloride but I am trying to find a way of doing it the easy way like with conductive paints, which are also suggested on the forum to work.

The object we would be plating for the customer is a hemisphere 40 inches in diameter and made of plastic, the customer wants to make from 2 hemisphere 1 big sphere for a Van de Graaff generator and because 40 inch metal spheres are so expensive he decided to make them from plastic and have them plated.

Now my question is not about how to do it or which coating works best but how much can the resistivity of the conductive coating be for the electroless nickel plating to be successful. The customer has some coatings that have resistivities in the order of 1000 to 2000 ohms/sq. Would this still be able to work or is the resistivity to high for the electroless plating process.

And Also would this coating be able to be used in the conventional electroplating.

Thanks in advance for any answers
Elmer Wiersma

Elmer Wiersma
plating shop employee/engineer - Amsterdam, Netherlands

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Remember that when we say "Electroless Nickel" we actually mean "Autocatalytic Nickel", a plating solution which will catalytically plate out on itself and on SOME other metals. It probably will not plate out onto a conductive copper paint without "sparking to start" regardless of resistivity.

I think that what you will want to do is metallize the plastic inexpensively with some kind of paint and then electroplate it rather than electrolessly plate it. Probably the biggest difference between using a conductive paint vs. a conventional palladium/tin chloride activation will be adhesion. Top quality plastic plastic is done by etching ABS or other plastic before the palladium/tin is applied. If your conductive paint sticks well enough, I think you can electroplate it. I'd suggest sulfamate nickel because it will be a low stress plating less likely to pull the paint off the plastic. Send pics!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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Hi Ted

I think you are right that the correct way to do electroplating the conventional way on a conductive paint, well the customer has found some conductive paint it is called electrodag 437 from achesion. That has a 0.5 ohm/sq resistivity, which is quite low. The best substrate for the paint is plastic so I think the paint should stick well.

The customer is trying to get some electrodag 437 in smaller amounts than 5 kg (about 10 pounds) because he does not need that much, 1 kg (2 pounds) would be enough to coat both hemispheres and they only sell the stuff in quantities of 5 kg. We then probably try some electroplating on inexpensive PVC pipe and if that works and the customer has finished making the hemispheres we could plate them. The customer just finished the mould and it needs to dry and the plastic company where he gets the material is open again on 13 august so it can take a while.

I will send you pics of the PVC pipe and hemisphere when they are plated, I wonder how it will turn out.

Best regards

Elmer Wiersma
- Amsterdam, Netherlands
2007

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I like your project. Good luck. Could I get some pics of it too?
Best regards

Jose Castellanos
- Minneapolis, MN, USA
2007

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2007

Hi

We have paints with a resistivity of 0.01 to 0.03 Ohms/square. These are silver containing.

Why not just paint the sphere with that and not worry about the plating?

Jim Rowbotham
- Halifax, West Yorkshire, England

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Hi All

Sorry for such a late answer but the customer has been very busy doing all sorts of things and had little time working on the project.

Unfortunately the customer, does not need to plate a plastic sphere anymore, he has tested various plastic but they are just to hard to form the to the mould he has build. He continues the project but now plans to impregnate a a polyurethane foam with polyester resin and so create a hard hemisphere when everything has set. This works he said on various test pieces.

He also tested if the foam with polyester resin could resist the temperatures of plating which would be around 60 to 70 °C but the foam becomes weak and you can penetrate it quite easily and so that is no use.

He also came up with the idea of just straight painting the hemisphere and not worry about the plating anymore unfortunately, it would have been great to see if it actually worked.

Elmer Wiersma
- Amsterdam
2007