Effect of Molecular Weight (MW) on the Performance of Polyester-Melamine Coil Coatings

Polyester-melamine coil coatings must withstand large deformations when formed into components. Increasing MW decreases the number of crosslinks formed and T_g. At temperatures well below T_g increasing MW decreases Young’s modulus and yield stress. Around T_g increasing MW increases the strain to failure. The formability has been assessed using Erichsen cupping tests over a wide temperature range, highlighting distinct transitions. A relationship between structure and properties is proposed. The greatest effects of MW are observed at temperatures in the glassy region. Understanding this behaviour allows optimal forming conditions to be chosen for a given coating.