Reactivity and curing efficiency of isocyanate cross-linkers with imidazole-based blocking agents for low-temperature curing of automotive clearcoats

Moonhyun Choi, Maeng Gi Kim, Kevin Injoe Jung, Tae Hee Lee, Miran Ha, Woochan Hyung, Hyun Wook Jung, Seung Man Noh

Research output: Contribution to journalArticlepeer-review

Abstract

For the application of low-temperature curing on automotive clearcoats, isocyanate cross-linkers blocked with imidazole derivatives were newly synthesized. The effect of the alkyl groups in the imidazole derivatives on the deblocking behavior and curing kinetics was investigated. The free isocyanate groups exposed by the deblocking of imidazole-based blocking agents were monitored by real-time Fourier-transform infrared spectroscopy. The bond dissociation energy, activation energy of deblocking, and H–N distance were interpreted through density functional theory simulation of various imidazole-based blocked isocyanates. To evaluate their applicability to automotive clearcoats, the synthesized imidazole-based blocked isocyanates were mixed with a polyol binder containing hydroxyl groups, and the clearcoat samples were cured at relatively low curing temperatures (100, 110, and 120C). The real-time storage modulus was measured using a rotational rheometer to elucidate the thermal curing dynamics by the blocking agents. In addition, the surface hardness of the cured clearcoat layers, which is affected by the chemical structure of the imidazole derivatives, was evaluated by nanoindentation test. In-depth analyses of the deblocking behaviors and thermal curing properties of clearcoats using imidazole-based blocked isocyanates demonstrated that the newly developed coating system could be suitably applied for the development of low-temperature curing technology.

Original languageEnglish
Article number974
Pages (from-to)1-11
Number of pages11
JournalCoatings
Volume10
Issue number10
DOIs
Publication statusPublished - 2020 Oct

Keywords

  • Automotive clearcoat
  • Blocked isocyanates
  • Cross-linking properties
  • DFT simulation
  • Imidazole blocking agent
  • Low-temperature curing
  • Urethane reaction

ASJC Scopus subject areas

  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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