How metal-plating on plastics is performed?

Question

Metal coated plastics are commercially abundant now-a-days. I want to know how they're plated.

Before posting, I did a quick search and found a nice link. It refers to this process as metallization, although I'm not convinced by the term. Is it right ?

That site already provided the basic information. However, it would be great if someone can mention a few examples(which metal/plastic used) for the various methods deployed.

Answer 1

I couldn't comment on the name. I am familiar with vacuum deposition, but i have only come across deposition on silicon, not plastic. the substrate ad metal are put in a vacuum chamber, the vacuum means that now the metal can be evaporated at a much lower temperature, and is then deposited onto the substrate.(see link)

I did an experiment of electroless plating of plastic with nickel. I can't say what plastic it was, probably PS or PP. usually electro plating requires electrodes and current to flow between them. electroless plating uses a electrochemical reaction in which a metal precipitates. Due to the treatment of the plastic the metal prefers to precipitate onto the plastic (this is a very simplistic information see liks for more information if you're interested)

the method I used in my experiment: the plastic is cleaned by diping it in a base bath (sodium carbonate, trisodium phosphate, sodium hydroxide), this is mostly to remove oily debris .

• Etching: ...etches the plastic to create microscopic pores that improve adhesion of metal and following steps

• Sensibilization: plastic is dipped in ti solution, keeps the palladium at its reduced state (next step)

• Activation: plastic is dipped in a palladium solution, Palladium catalyses the formation of nickel particles.

• Plating: since there is no current flowing another particle has to be oxidized for the nickel to be reduced. in this case the reaction used is oxidation of hypophosphite to phosphite

The result was a very nice metallic finish.

more information:

• Electroless nickel plating on Wikipedia
• plating kit
• plenty of information on electroless deposition
• evaporation-deposition

Answer 2

That recipe is taken from book dedicated to chemical restoration techniques: ISBN 5-7245-0274-7, 1990.

Method 1.

1) AgNO3, 5g + water, 60ml. Divide to 20 and 40 ml solutions.

2) 40ml of Solution(1) + NH4OH, slowly, active mixing. Dark precipitation occurs.

3) Solution(2) + 20ml of Solution(1), add 5ml per 2 sec. Then add NH4OH. You obtain cloudy solution (otherwise, add more AgNO3 solution).

4) Solution (3) diluted up to 500ml.

Now we can reduce Ag to obtain metalic layer.

1) Refined sugar, 75g + water, 500-600 ml

2) Solution(1) + H2SO4, 10ml, 10%. Boil for 5-6 h

3) Solution(2) becomes dark-yellow. Cool it.

4) Dilute soluion(3) up to 1L.

5) Before using dilute 10 times.

When you mix 2 solutions Ag is reduced as precipitate: Ag(NH3)2OH -> Ag + NH3 + OH-