This article was co-written by Elizabeth Kidd, BTG Labs' Custom Applications Scientist and Research and Development Chemist.
Coating and adhesive bonding are extremely common manufacturing process steps. It may seem obvious, but to ensure success in these applications, surfaces must be properly cleaned or manufacturers run the risk of bonding and coating failures. Simple enough, but if that's all there is to it then why do failures in these applications still occur?
What does it actually mean to have a clean surface?
Industry has the bread of this sandwich figured out. There are proven and widely used methods for controlling adhesive and coating composition as well as controlling the application and curing process. But a key ingredient is lacking—a relevant definition of the word “clean” as it relates to the quality of the surface state.
The current industry standard of “clean” does not consider true surface cleanliness. Instead, “clean” is determined by monitoring process parameters. For example, take the parts wash Millipore test. This test quantifies the amount of particulates in a wash tank by filtering a sample of wash solution through a filter paper and measuring the dry weight of the filter paper before and after. This test provides some information about the wash tank solution but gives no indication of chemical cleanliness of the part surfaces exiting the wash.
How can we evaluate chemical cleanliness?
The methods used to determine if a surface has been properly prepped (such as dyne ink, water break tests and other destructive laboratory methods) have proven themselves to be costly, ineffective and a dead end when it comes to truly understanding what is causing adhesion failures. For those of us concerned with process efficiencies, what are we to do?
Consider the top few molecular layers of a surface—the surface that you can’t see and won't be evaluated by any of the aforementioned methods. If you have a layer of—for lack of a better word—molecular crud (left hand portion of the below image) covering up your baseline material, it’s likely you’ll run into difficulties when bonding or coating. However, if you’ve successfully created a surface that’s clean on a chemical level (right hand portion of the below image) you’re bound to have greater adhesion success.
We must redefine the industry standard of “clean”.
At BTG Labs we have the experience and the equipment that can help you take control of your cleaning process. For more information about how you can stop guessing and start managing your whole process, download the our step-by-step eBook guide to addressing the sources of contamination plaguing your process: Checklist: Adhesion Failure Root-Cause Analysis for Manufacturers.