Synthesis and formability of long alkyl chain of polyester for automotive pre-coated metals

Abstract

Purpose Formability is an important property of automotive pre-coated metals (PCMs). The purpose of this study is to investigate the effect of long alkyl chains of polycarbonatediol to control the formability of polyester coatings. Design/methodology/approach Polyester resins with long alkyl chains were synthesized using different contents of polycarbonatediol. These resins were characterised by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (1H NMR) and fourier transform infrared spectroscopy (FT-IR). The polyester coatings were characterised according to their viscoelastic behaviour, formability, flexibility and anti-corrosion property. Findings The tensile strength of PCM should be larger than 5.6 MPa of the compressive stress at a strain of 23.4 per cent to overcome the harsh condition of deep drawing. To analyse the formability, Fε (forming coefficient based on strain) and FU (forming coefficient based on strain energy) were calculated. When Fε and FU were larger than 1, the polyester coatings exhibited good formability. Research limitations/implications Long alkyl chains of polycarbonatediol gave flexibility and good formability to the polyester coatings. Practical implications There are two conditions that lead to the good formability of PCM. One is tensile strength and the other is forming coefficients based on strain and strain energy. Originality/value Long alkyl chains of polyester were a major factor to improve flexibility and formability. Thus, to have good formability, the tensile strength of PCM should be larger than 5.6 MPa, and the forming coefficients should be larger than 1.