Two batches of Valox VX 5005 (blend of PBT, PC and EPDM) pellets containing about 5% glass fibers. First batch: poor adherence of paint film. Second batch: good adherence
Measuring cell: DSC20
Pan: Aluminum standard 40, pierced lid
Sample preparation: Disk cut from pellet (first batch 6.7 mg, second batch 14.4 mg)
DSC measurement: Heating from room temperature to 300°C at 10 K/min
Atmosphere: Nitrogen, 50 cm3/min
The content of slip additive is proportional to the heat of fusion of the peak around 100 °C. The first batch gives a value of 8 mJ. This corresponds to approx. 1.2% slip agent (assuming a heat of fusion of the additive of 100 J/g).
If injection-molded parts have to be painted, the presence of additives in the polymer may influence the adherence of the paint film. Additives such as waxes undergo crystallization can be detected by their DSC fusion peak.
Adherence of Paint on a PBT Blend | Thermal Analysis Handbook No.HB256 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics