Summary for corrosion on plated plastic Discussion
Corrosion on plated plastic is the core issue here: a vendor’s cosmetic plastic parts are failing a 168-hour salt spray test with greenish discoloration, fading, cracking, and flaking after a nickel/copper/nickel/nickel stack and a gunsmoke or gold finish, followed by electrophoresis for UV protection. Ken Vlach suggests the green-blue color may indicate nickel corrosion and notes that internal stress in the plating could be part of the problem; he recommends testing parts without the electrophoresis layer, inspecting under magnification, and doing bend and corrosion tests. He also suggests trying Incralac or another more suitable clearcoat, and mentions a modified polysiloxane coating as a possible but not yet widely available option. A later reply says the protective film is failing, so the answer is to use a thicker or more resilient coating; a conversion coating may help adhesion but will not solve the issue alone, and the lacquer supplier should be consulted for a process that meets the test requirement.
Our vendor is having a problem plating some plastic cosmetic parts to withstand 168 hour salt spray test. The results show discoloration
(greenish color), fading, cracking & flaking. The process they are currently using is; nickel plate–copper plate–nickel plate & then another nickel plate for more binding energy and then a gunsmoke or gold color plating. They then finish with an electrophoresis treatment for UV protection. Do you have any suggestions on how we can prevent these problems?
Tim Stutzman
fishing tackle – Philadelphia, Pennsylvania, USA
2005
A. Gunsmoke is? How is it affected by the salt spray?
Greenish or blue-green corrosion?
Nickel needs UV protection?
I’m not a POP expert, but suggest there may be high internal stresses in the plating. Also, the nickel might resist corrosion better w/o the copper and “gunsmoke.”
1) Check some parts w/o the electrophoresis (acrylic or PU clearcoat?) examine under magnification, do some bend tests, corrosion test.
2) Suggest replacing the clearcoat with Incralac
⇦ on
eBay or
Amazon [affil link]
®, an acrylic lacquer containing benzotriazole, a corrosion inhibitor. Developed to protect bronze sculptury, etc.; lasts up to 13 years outdoors. A modified polysiloxane coating is also described, but maybe not yet commercially available. www.copper.org
Ken Vlach [deceased]
– Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
The greenish colour is due to the nickel metal being corroded. This will in turn result in lifting of the protective films. Clearly the protective film is not doing its job, so you need to either apply a thicker coat or find one that is more resilient to your 168 hour salt spray test. You may get some help form a conversion coating, but it will not solve your problem by itself; another benefit of selecting the correct coating is that it can help in the adhesion of your lacquer. Talk with your lacquer supplier – it is their job to sell you the best available process to meet your needs; after all, you’re paying for their services!
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2006