Surface Preparation Considerations When Plating onto Plastic

When most of us think of electroplating, we think of techniques involving the coating of a metal part with another metal material such as gold, nickel, copper or silver. However, it is also possible to plate non-metallic materials to promote electrical conductivity, improve corrosion protection or enhance the aesthetic appeal of the finished part.

Plastic is one of the most common non-metallic substances that can benefit from electroplating, including popular plastic resins such as polycarbonate, polyethersulfone, Teflon and diallyl phthalate.

What Are the Challenges of Plating on Plastic?

The inherent challenge with plating on a plastic substrate is that plastics do not conduct electricity. Therefore, the electrically charged metal ions produced by the DC current during the plating process will not adhere to the surface of a plastic work piece. Consequently, it is necessary to prepare the surface by depositing a conductive film prior to executing the traditional electroplating process.

There are several techniques that metal finishers used to prepare and activate plastic surfaces for electroplating:

• Etching: The etching process was developed in the 1960s to promote adhesion when plating acrylonitrile butadiene styrene (ABS), a polymer that is used in the manufacturing of various automotive products, medical devices, electronic assemblies as well as household and consumer goods. Etching entails the application of a chromic acid-based solution to remove the butadiene component from the resin, which facilitates bonding with the metallic coating.
• Electroless plating: Electroless plating is an alternative form of plating that relies on an autocatalytic chemical reaction instead of electricity to apply the coating. Nickel and copper are the materials that typically serve as the base metal for the electroplating process. This technique also provides a uniform coating and enables the plater to control the coating thickness more efficiently.
• Corona discharge: A corona discharge is a physical process that generates ionized air, which reacts with the plastic surface to develop free radicals. The radicals subsequently react with the oxygen in the atmosphere to increase the plastic substrates surface energy and promote bonding.
• Flame treatment: The flame treatment technique introduces the plastic surface to a gas flame, which results in oxidation and increases surface energy. This technique must be implemented with extreme caution — exposing the substrate to the flame for more than a few seconds will cause warping.
• Plasma treatment: Plasma treatments are executed under a partial vacuum. They entail the activation of a gas plasma which produces “excited species” that react with the surface of the substrate. This technique typically promotes better surface stability than other chemical or physical treatment processes.

Learn More from the Experts at SPC

At SPC, we’ve developed an effective process for “metallizing” various plastics, which includes the implementation of the most appropriate surface preparation techniques for your plastic material of choice. Contact us for more information today.