PREPARATION OF MEDICAL DEVICE SURFACE FOR ADHESIVE BONDING

PROJECT BACKGROUND

The 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 is required to clean the surfaces prior to coating or bonding.

THE PROBLEM

A 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.

ANALYZE’S APPROACH TO RESOLVING THE PROBLEM

ANALYZE suggested that water contact angles would be a good measure of the part’s surface cleanliness. ANALYZE identified a contact angle measuring instrument that would be appropriate to the environment in which it would be used. The client purchased the instrument and shipped it to ANALYZE where members of the technical staff developed the QC methodology using client supplied samples. The results of the contact angle measurements were correlated to ESCA analyses of the surface and adhesive bond strength. At the conclusion of the methods development phase, the QC protocol and instrumentation were transferred to the client’s facility.

THE RESULT

Static and dynamic water contact angles could be measured easily and documented with digital images in a timely manner. The following images show typical magnified images of the D.I. water drop immediately after the drop had been deposited onto the part surface from the tip of the micro-syringe. The two images show the drop on the part surface before and after cleaning.

Before Cleaning



After Cleaning

Studies 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^o-55^o) to additive covered surfaces (101^o-108^o) in a matter of days.

CONCLUSION AND BENEFIT TO THE CLIENT

The objective of the program was achieved and the client had a QC method to qualify part surfaces and/or cleaning process changes for the adhesion bonding operation. 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.

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