I wanted to comment on the question about painting of plastic parts that a reader submitted to you. Here are some huge points to look at when you have these issues.


Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

Q. I read PF every month, and I wanted to comment on the question about painting of plastic parts that a reader submitted to you. Some huge points to look at when you have these issues:


  • Operators using hand lotion on their hands then handling the parts. This can be helped by gloves, but the lotion can still seep through to the parts if they use excessive amounts.
  • A change in mold release used in the plant, or operators using excessive amounts. Even when the parts are rinsed, release agents can wreak havoc. Silicone or zinc-based mold release agents can build up on the molding surfaces.
  • Tool surfaces not being cleaned of mold saver (rust preventative) before production beginning.
  • Internal mold release agents,. Many resins contain internal mold releases. If the plastic is not compounded as usual or if the resin is over-dried or overheated during processing, you can have adhesion issues.
  • Molded-in stresses are the last quiet generator of scrap. While molding interior parts for a European auto manufacturer, in a past life, we had some strange paint adhesion issues. We sprayed the parts with a mold cleaner and the high stress area became evident when the surface began to look like wind-blown sand dunes. We increased the mold temperature to remove the hidden stress, then made sure that this test was performed every four hours during production.

I hope your readers find this?useful. R.B.



A. Thank you for taking time to write and share this information. The five points you raised will certainly help finishers identify and solve problems in their shops.

It’s important to note that point 1), painters’ use of hand lotion, applies to finishing not only plastic but all substrates. This is often overlooked.


  • The Importance of Particle Size in Liquid Coatings

    Coating problems and solutions associated with particle size reduction...

  • Zinc Phosphate: Questions and Answers

    Specific questions about zinc phosphate and pretreatment are answered in one article...

  • Masking for Surface Finishing

    Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.