AIC coating application engineers discuss the best polymer coatings with high continuous operating temperatures, and some of the application issues that can cause coatings to fail at high temperatures.
These days, polymer coatings are not well-known for their high operating temperatures. That’s primarily because many ceramic coatings outperform polymer coatings in this aspect, withstanding operating temperatures of up to 1300 °F and more.
But from an engineering perspective, polymers often offer a more desirable combination of properties. And some polymer coatings can withstand some pretty high operating temperatures, when applied correctly. Here’s a quick primer on which polymer coatings are truly high temperature coatings.
Polymer Coatings with High Operating Temperatures
One of the polymer coatings with highest operating temperatures is PES (polyethersulfone), which can stand operating temperatures up to 550 °F and brief exposures up to 700 °F. The coating is also known for providing some corrosion protection. Although PES can withstand extreme heat, it doesn’t offer many of the combinations of properties that other, more developed polymers can offer.
Most PTFE– and PFA-based coatings can withstand operating temperatures up to 500 °F, while keeping all of the properties that make them so popular: nonstick and low friction properties, wear resistance, weather resistance, corrosion resistance and pliability. Most of these coatings will perform under high heat even when applied as extremely thin films. FEP coatings, which offer similar properties to PTFE and PFA coatings, usually can only withstand up to 400 °F. (For an explanation of the similarities and differences among PTFE, PFA and FEP, see our brief overview.)
Xylan® coatings, a series of PTFE coatings created by Whitford, are particularly known for their excellent resistance to extreme temperatures both cold and hot. Many Xylan coatings can operate in temperatures up to 550 °F. (See Whitford’s info on Xylan® here, or take a look at our Xylan® coating services here.)
For those looking outside the PTFE family, PPS (polyphenelyne sulfide, known by the brand name Ryton®, developed by Chevron Philips) can offer operating temperatures of up to 500 °F, depending on what chemicals the coating is exposed to at that temperature. The coating is used frequently in the chemical processing industry because of its excellent resistance to chemicals and its mechanical toughness. (Ryton® is now produced by Solvay Plastics, more info about it can be found here.)
Application Issues that Can Affect High Temperature Coatings
The number one issue that can cause a coating to fail at high temperatures is the failure to properly cure the part. We won’t go into all of the elements that affect curing here, but curing is not always a straightforward process, and often takes detailed calibration on the part of an experienced coater. If you are having a high-temperature failure from a coating that is designed to withstand the heat, we suggest starting with a thorough review of the curing process. (Even if your coater insists that the curing is fine.)
Another frequent performance issue that can emerge with high temperature coatings is blistering. The root cause of blistering at high temperatures is almost always too much coating applied in a single layer. A coating will blister at high temperatures because of trapped solvents trying to emerge. Those solvents are almost always trapped when the skin of a too-thick layer of coating dries before the solvents have a chance to escape. Anyone experiencing coating blistering should look at the thickness of the coating and whether that thickness would be better achieved by applying the coating in more layers.
If you are experiencing a coating failure that you can’t figure out, or if you are looking for a recommendation for a good high-temperature coating for your part, don’t hesitate to give us a call.