Effect of cycloaliphatic structure of polyester on the formability and stone-chip resistance for automotive pre-coated metals

• Synthesized of cycloaliphatic structure of polyester with 1,4-CHDA.
• Cycloaliphatic structure of polyester coatings enable at 30 mm at the deep drawing.
• BCHDA-20 had good elongation value, formability, and chipping resistance.
• Cycloaliphatic structure gives better elasticity than aromatic structure.

Four types of cycloaliphatic structure of polyester were synthesized, using 1,4-cyclohexanedicarboxylic acid (1,4-CHDA). Those resins were formulated to make polyester/melamine coatings to control the formability, and to have good stone-chip resistance. The characteristics, viscoelastic behavior and flexibility of those resins were measured by DMA and tensile test. Cycloaliphatic structure of polyester coatings were coated on the cold roll steel sheets to verify formability, using a deep drawing test and stone-chip resistance was measured by the chipping resistance test at the −20 °C. Results showed that storage modulus decreased, and glass transition temperatures shifted to lower temperatures with increasing contents of cycloaliphatic structure. So, cycloaliphatic structure of 1,4-CHDA provides lower stiffness and higher softness to the polyester coating and has better elasticity than aromatic structure of IPA. To analyze the formability, we calculated FU (the forming coefficient based on strain energy) and Fε (the forming coefficient based on strain). When FU and Fε are both larger than 1, the polyester coatings have good formability. Also, BCHDA-20 had 0.44% of removed area by the chipping resistance test and it means that cyclic structure of 1,4-CHDA has better elasticity than aromatic structure, and can give better impact resistanceFrom those tests, BCHDA-20 which had 20 mol of 1,4-CHDA had good formability and also showed good stone-chip resistance. So, cycloaliphatic structure provides lower stiffness and higher softness to the polyester coating for automotive pre-coated metals.