Part 1: The Basics of Pressure Sensitive Adhesive (PSA) Failure
When considering Pressure Sensitive Adhesives, you must look at many aspects including the failures. Engineers always look at all aspects including failures to avoid something going wrong. This two part series will address the language, importance of surface cleanliness, and the application of a PSA.
To begin, let’s agree on some language. If you have a part with a sticky adhesive coating on one or both sides, we are going to call that sticky coating PSA. It’s an acronym for Pressure Sensitive Adhesive. We can classify the purpose of the Pressure Sensitive Adhesive (PSA) into two functional segments; Assembly Aid or Permanent Fastener.
The assembly aid PSA is where the PSA acts as nothing more than a sticky means to hold a part in place long enough to allow completion of an assembly process. Once assembled, the PSA serves no function since the die cut part is mechanically constrained in the assembly. The second category, and most critical is where the PSA performs the same function as a mechanical fastener.
Across the board, industries are moving away from screws and rivets where a PSA coated part can perform the same function with less weight, easier assembly and design traits not possible with a mechanical fastener. This all sounds good except what happens when a PSA part doesn’t stick the way it did when originally designed, or the PSA part falls off in service?
I can tell you without hesitation that nothing gets more attention for the failure than the PSA. What else could it be, the customer swears they didn’t change a thing and now because the parts don’t stick it can’t be anything other than the PSA. The PSA manufacturer or the die cutter who was applying the PSA changed something.
It is impossible for it to be anything else… or is it? Here are some basics on what JBC Technologies discovered when the PSA suddenly stopped functioning as intended.
PSA simply doesn’t work without some basic practices. Whether used as an assembly aid or permanent fastening PSA, surface preparation is important.
Surfaces to be bonded must be clean, free of dust, dirt, lint and oils. In one situation where parts suddenly failed to stick, it was discovered that the customer changed mold release used to assist part removal from an injection mold.
It was never discussed or tested down the line and when parts suddenly stopped sticking all the blame was placed on the PSA. When queried if the customer had changed anything that could lead to poor adhesion, the answer was no. In their mind nothing changed. They had always used mold release and had no reason to think it negatively affected the PSA.
In part 2 of this post, we will look into the application of PSA and how that affects the bond performance. Stay tuned.