Case Studies

Automotive Air Conditioning Button Breakage

Problem:	Breakage occurs during durability testing of new model plastic buttons. Why doesn’t current model product fail under same test conditions?
Approach:	Material in “good” and “bad” buttons were evaluated and compared. Differential Scanning Calorimetry (DSC) was performed to determine the thermal history and the degree of crystallinity of the polymer material to detect anomalies of the material’s thermal behaviour, caused by internal stresses during processing. Compositional analysis and inorganic filler content were performed by Thermal Gravimetric Analysis (TGA).
Conclusion:	We determined that the primary resin of both samples was polycarbonate. Thermal prehistory differences were found in the two batches, indicating the presence of built in stresses in the “bad” button that resulted in failure. Due to the specific molecular structure, polycarbonate resin is particularly prone for development of internal stresses during non-optimized processing conditions during injection molding.
Benefits to Customer:	Increased reliability of AC unit buttons.