Real-Time Measurement of Thermal Curing Reaction of Automotive Paint Using FTIR

Importance of the Topic

Automotive paint curing is a major source of CO₂ emissions in vehicle manufacturing. Real-time monitoring of the thermal curing reaction helps determine optimal temperature and time conditions, contributing to energy savings and CO₂ reduction in line with global carbon-neutrality goals.

Study Objectives and Overview

This study employed Fourier Transform Infrared (FTIR) spectroscopy with a heated attenuated total reflection (ATR) accessory to track, in real time, the polymerization of an acrylic urethane automotive paint. The goal was to identify efficient curing parameters that minimize energy use without compromising paint performance.

Methodology and Instrumentation

• FTIR spectrometer: IRTracer™-100
• Heated ATR accessory: MicromATR single-reflection diamond disk (room temperature to 130 °C)
• Measurement parameters: resolution 4 cm⁻¹, 20 scans, wavenumber range 4000–400 cm⁻¹, Happ-Genzel apodization, DLATGS detector

Sample preparation involved mixing the acrylic polyol main agent and aliphatic polyisocyanate curing agent at a 10:1 ratio. A single drop was placed on the heated ATR prism for continuous measurement.

Key Results and Discussion

Spectral changes were observed at the isocyanate peak (~2270 cm⁻¹) and the methyl reference peak (~2940 cm⁻¹). The reaction rate DR was defined as 1 – [R(t)/R(0)], where R is the isocyanate‐to‐methyl peak ratio. Time-course measurements at constant temperatures (40 °C, 60 °C, 80 °C, 100 °C) showed rapid curing at 80 °C and 100 °C, reaching DR ≈ 0.8 within 30 minutes. Below 80 °C, curing was slower, requiring over 2 hours to approach equivalent conversion.

Benefits and Practical Applications

• Identification of 80 °C as the optimal curing temperature balance between speed and energy efficiency
• Reduced CO₂ emissions through shorter bake cycles
• Minimal sample volume needed due to single-drop ATR measurement
• Applicability in paint formulation development, process optimization, and quality control

Future Trends and Opportunities

Further integration of real-time FTIR monitoring into automated industrial curing ovens could enable closed-loop control. Expanding this approach to other coating chemistries and employing advanced data analytics or AI models may lead to even greater process efficiency and sustainability in surface treatment industries.

Conclusion

This work demonstrates that FTIR with a heated ATR accessory provides a robust, real-time analytical tool for optimizing thermal curing of automotive paints. The method identifies 80 °C as an effective cure temperature, offering a path to lower energy consumption and CO₂ emissions.

References

1. Nissan Shatai Co., Ltd. Environmental & Social Report 2020.
2. K. Mori, “Method for Estimating Crosslink Density in Curing Process of Coatings Films – Proportionality between Storage Modulus and Crosslink Density,” Journal of the Japanese Society of Colour Material, vol. 86, no. 4, pp. 123–127, 2013.