This is the third of an ongoing-series of case studies from my experience, looking at problems in Design and Manufacturing and how a solution was achieved. Parts I and II are here and here, respectively.
As a part of a material cost reduction team in the climate control division of Visteon Corporation, I had joined the group just as several large projects were coming to fruition. One, under the direction of another team member, was the replacement of a nylon material with a polypropylene material for the housing of a control panel for a high-volume automotive air conditioning product. All the testing had been done to verify that the direct substitution of one material for another, lower-cost, material did not compromise product performance, durability, or the ability to produce it from raw materials to final product… a dock-to-dock approach to the validation of a new material was often required for this kind of project.
It was in this last phase – when hopes were high for this cost-savings project, with a projected annual cost savings of over $200K per year – that the project hit a snag. Each piece had a code sprayed on it with the production date and other important tracing information on it.
Essentially, although the ink would dry in place as before, it was not adhering to the surface as before and would easily smudge; thus, the necessary information the markings contained would be obscured. This should have been expected; polypropylene, like all polyolefins, has a very low surface energy which makes it hard for inks and glues to adhere to it.
The most common surface treatment for this is a primer. Essentially, the process goes like this: a choice is made for a polyolefin in a product; a component that needs to be glued to another. In talking with a glue maker, who should do due diligence in understanding the application, the substrates being glued together will be mentioned. Immediately a concern about adhesion will be voiced and – lo and behold! – the glue maker has a solution: a primer.
Certainly this makes sense from the glue maker’s point of view. They come across as proactive, voicing a concern for the application and having a ready-made solution available. The ink maker similarly proposed a primer, also of their own manufacture (clearly they’d seen this situation before!). But this was an open-air existing assembly line; there was no room to put in an enclosure to spray a volatile-based primer upstream of the marking process. Never mind that the design and engineering of such an enclosure would take significant time, add a material requiring toxicology approval to the plant’s mix, and the capital cost and ongoing variable cost of the new material being applied would significantly eat into the projected savings.
But based on my own experience and having taken a continuing education class, Adhesives and Adhesion, at U Mass/Lowell, plus other research I had done faced with similar gluing problems I knew there were other solutions: flame, corona, or plasma treatment.
I quickly researched and found a corona spray equipment company – it was not a “Joe’s Fish, Chips, and Corona-Treatment Equipment” company, but a well-established one with some longevity. Their sales representative visited, saw the line and the application, and arranged for a loaner unit to be overnighted to the plant. It was quickly installed and test pieces were run down the line, each unit spending several seconds being sprayed by the ionized coronal discharge directed at the precise location of the markings.
And it was a smashing success. Not only did the ink adhere initially and not smudge, but in the aging and “shake and bake” tests done, the markings lasted as durably as the ones on the original nylon substrate, which were tested side-by-side with the new pieces to ensure an apples-to-apples comparison. This project went from “show-stopper crisis” to success… because I knew something nobody else on the team did – thus highlighting, yet again, the benefits of hiring from outside.
- Adhesion to plastics is a common problem, especially low-surface energy materials like polyolefins
- Glue makers will understandably race to recommend a chemical primer
- In many instances other techniques exist to enhance the surface energy to get better wetting and adhesion
Before running to add yet another chemical to the production mix, along with its own MSDS, traceability, and hazards, consider corona, plasma, or flame surface treatments when faced with a problem of poor adhesion to plastics or rubbers.
For reference and information, here are two articles about adhesives and surface treatments – from the medical device world, but certainly applicable everywhere.
© 2013, David Hunt, PE