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A comparison of the stick-slip behavior of an uncoated rubber test-piece and its Xylan 2020 counterpart shows the forces required to move the test-pieces across a glass or painted surface at constant speed. The peak force values (spikes in the trace) of the uncoated sample represent its tendency to stick as it's pulled across the surface. This stick-slip phenomenon often leads to the squeak and itch noises generated by seals moving against car bodies when vehicles are in motion. |
APU lubricant that mimics the noise suppression and release properties of the best performing silicones has been developed by Whitford Worldwide, West Chester, Pa. It is used in a new line of weatherstrip coatings called Xylan 2020.
Silicone coatings have for years served as noise-free lubrication on automotive EPDM sealing systems. But these coatings have some drawbacks. They are usually thin and soft so they can wear off from abrasion. Rapid wear causes loss of lubricity and of release properties needed for a quiet seal. Silicones are also hydrophobic — lacking an affinity for water. They tend to pass this hydrophobic quality to other surfaces in the workplace which then become difficult to paint or polish.
To overcome such shortcomings, designers often turned to conventional polyurethane (PU) coatings which are inherently tough yet flexible. Typically PUs are hydrophilic (water absorbing) which makes them a bit noisy. Manufacturers of such coatings add polytetrafluoroethylene (PTFE) to help abate noise, but usually with limited success.
The new lubricant used in the Xylan 2020 seals is a single-component, waterborne PU which needs no PTFE additive to help suppress noise. As a single-component system, the Whitford lubricant needs no mixing as with solvent-borne silicones (which may need as many as five components) and conventional PUs (needing at least two). Being waterborne, Xylan 2020 coating does not use the highly toxic, free isocyanates needed by conventional nonwaterborne PUs during manufacture.
Many flexible coatings tend to be highly sensitive to curing temperature/time. In contrast, Xylan 2020 coating has a much wider curing process range. It complies with stringent automotive performance specifications and is VOC compliant.
Information for this article was provided by Whitford Corp., West Chester, Pa., (610) 296-3200, www.whitfordww.com