Project BackgroundThe presence of foreign contamination on surfaces to be coated or adhesively bonded may interfere with both the initial and long term integrity of the bond. Significant effort may be required to clean the surfaces prior to coating or bonding.
The ProblemA medical device manufacturer was experiencing variability in the strength of an adhesive bond to a part molded from a thermoplastic resin. The manufacturer had determined that a known additive in the bulk of the polymer was diffusing to the surface and creating a thin ‘release’ film on the part’s surface. Due to other requirements, the additive could not be removed from the formulation. It was established that if the surface was sufficiently clean to achieve good initial adhesion, the long term adhesive strength of the bond was also retained under a variety of environmental testing conditions. ANALYZE was asked to develop a simple, reliable, quantitative QC procedure that could be used to qualify parts for adhesive bonding in the manufacturer’s production facility on a daily basis.
AfterStudies were done as a function of surface cleaning methodologies and part conditioning. For instance, there was little change in the static contact angle values or the surface chemical composition as measured by ESCA over a 42 day period at room temperature. However, when the parts were heated at elevated temperature, the static water contact angles were observed to increase from those of ‘clean’ surfaces (44°-55°) to additive covered surfaces (101°-108°) in a matter of days. With modern contact angle instrumentation, operator training is easily done and the speed of the method allows 100% inspection if required. The capture of digital images and image analysis information (e.g., contact angle values) can be associated with a specific part in a quality system electronic archive.