PAINTING POLYPROPYLENE
We are working with flame pretreatment but are seeing inconsistencies. Adding to our confusion is the apparent lack of consistency from dyne solutions—we see wetting out of the dyne solutions from 35–70, but then the coating, which is a 38 dyne, doesn’t stick consistently.
Share
Q. I am the manager in charge of finishing and decorating operations at our plant. We are having an adhesion issue with one of our products. I read a few of your responses on PFOnline (www.pfonline.com) and have been impressed.
I would appreciate your thoughts on the following: We are working to achieve a variegated appearance on mineral-filled polypropylene exterior siding, the substrate being injected molded. Our objective is to use a single-part, water-based coating. Our issue is adhesion of the coating on the multifaceted surfaces. We are working with flame pretreatment but are seeing inconsistencies. Adding to our confusion is the apparent lack of consistency from dyne solutions—we see wetting out of the dyne solutions from 35–70, but then the coating, which is a 38 dyne, doesn’t stick consistently.
Featured Content
We were concerned about contamination, so in our tests we have been wiping the polypropylene parts down with isopropyl alcohol. Obviously, there is a great deal more background to this issue, but this is the simple overview.
Thanks for any help you can give us. M.B.
A. In flame treating, the flame must impinge on the surface to be pretreated. I can’t imagine that parts of the multifaceted surface of your product (exterior siding) are hidden from the flame (i.e., the flame can’t reach or touch them), but it may happen. Perhaps the isopropyl alcohol wipe is not helping. Instead, it may be adding to the problem by introducing and spreading contaminants. The other thing about isopropyl alcohol is that it evaporates quickly and may not wet the surface long enough to clean. For solvent wiping, I prefer using mineral spirits, changing wipers and solvent often. Furthermore, I suggest you read the comments by R.B. in “Plastic Painting Issues” elsewhere in this column for other possible solutions to this problem.
RELATED CONTENT
-
Improving Transfer Efficiencies in Coating Operations
There are many methods for addressing electrostatic grounding in metal painting processes, and Tim Ulshafer from Mueller Electric says the best method for your process is a simple and worthwhile exercise.
-
Understanding Paint Atomization
BASF coatings development expert Tim December explains how paint atomization works for both pneumatic spray applicators and high-speed rotary bell applicators.
-
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.
