Mix Ratio Identification in Industrially Significant Two-Part Coating Systems Using the Agilent 4300 Handheld FTIR

Importance of the Topic

Two-part (2K) coatings combine resin and hardener to deliver tailored protection and aesthetic finishes for automotive, industrial, and architectural applications. Precise mixing ratios are critical to achieve desired cure kinetics, mechanical strength, and long-term durability. Deviations can cause defects such as discoloration, poor adhesion, and early coating failure.

Aims and Study Overview

This study evaluates the Agilent 4300 Handheld FTIR system for rapid, on-site identification of mix ratios in epoxy and polyurethane two-part coatings, as well as a combined epoxy primer and polyurethane topcoat system. Calibration and validation samples were prepared with target and off-target resin-to-hardener ratios to build predictive models.

Methodology and Instrumentation

A series of epoxy and polyurethane coating formulations were mixed at recommended and varied ratios, applied to steel panels, and air-dried overnight.

• FTIR Instrument: Agilent 4300 Handheld FTIR
• Sampling Interfaces: External reflectance and diffuse reflectance
• Spectral Range: 4000–650 cm–1; Resolution: 4 cm–1; 64 co-added scans (26 seconds)
• Data Analysis: Partial Least Squares regression with mean centering and multiplicative scatter correction

Main Results and Discussion

Calibration models exhibited strong correlation (R2 > 0.99) using 5 factors for polyurethane, 6 for epoxy, and 4 for the two-coat system. Validation samples showed average prediction errors of 3.24% (polyurethane), 2.24% (epoxy), and 2.82% (polyurethane on epoxy) with external reflectance; diffuse reflectance results were similar. Key spectral bands at 2100–2400 cm–1 (polyurethane) and 1650–2200 & 1600–800 cm–1 (epoxy) were instrumental in quantifying curing agent content.

Benefits and Practical Applications of the Method

• Rapid, nondestructive mix ratio measurements directly on-site
• Portable handheld design ideal for field and production-floor quality control
• Intuitive software with preconfigured PLS models for users of varying experience
• Versatility across reflective and nonreflective substrates

Future Trends and Opportunities

• Extension to additional coating chemistries and cure systems
• Integration with cloud-based data management and reporting
• Development of predictive models for curing degree and performance monitoring
• Advances in handheld spectrometer sensitivity and miniaturization

Conclusion

The Agilent 4300 Handheld FTIR offers a reliable, fast, and portable solution for determining mix ratios in two-part coatings, supporting quality assurance and performance verification across laboratory and field settings.

References

Agilent Technologies, Inc. Application Note: Mix Ratio Identification in Industrially Significant Two-Part Coating Systems Using the Agilent 4300 Handheld FTIR, 2015.