Analysis of ink and paint using near-infrared spectroscopy

Significance of the topic

Near-infrared spectroscopy (NIRS) provides rapid, non-destructive analysis of inks, paints, pigments and dyes. Its ability to deliver real-time quality control throughout raw materials, process intermediates and finished products makes it vital for minimizing production failures and ensuring consistent product performance in the coatings and printing industries.

Objectives and Overview of the study

This bulletin presents a series of feasibility studies applying NIRS to key analytical challenges in the ink and paint sector. The objectives are:

• Quantitative monitoring of dye concentration in aqueous solutions
• Qualitative assessment of moisture in flush pigments
• Determination of moisture content in yellow pigment
• Simultaneous monitoring of color strength and viscosity in inks
• Detection of catalyst levels in black paint primer

Methodology and Instrumentation

All studies employ NIRS in the 1100–2500 nm spectral range, using a variety of sampling modes (transmittance, reflectance, interactance) and instrument configurations. Calibration models were built using PLS or single-wavelength approaches to correlate spectral features with analyte concentration or qualitative class.

Used instrumentation

• NIRS XDS RapidLiquid Analyzer (Metrohm) for transmittance measurements of dye solutions
• NIRS XDS SmartProbe Analyzer with fiber bundles for reflectance/​interactance moisture screening
• NIRS XDS RapidContent Analyzer Solids for reflectance analysis of pigment pellets and primer
• NIRS XDS Process Analyzer with remote reflectance probe for in-line ink viscosity and color strength

Main Results and Discussion

• Monitoring dye strength: Calibration at 1678 nm achieved SEC of 1 % over 90–122 % dye range in water solutions.
• Moisture in flush pigments: Qualitative models based on 1360–1500 and 1845–1990 nm regions successfully distinguished moisture classes across 19 samples.
• Yellow pigment moisture: PLS models at 1940 nm delivered SEC of 0.1 % for moisture between 0.3 and 2.6 % using both fine-ground and coarse sample cells.
• Ink color strength and viscosity: Dual calibration using 430–800 nm (color strength, SEC 1.6) and 400–2500 nm (viscosity, SEC 0.2 %) demonstrated simultaneous monitoring of two critical ink properties.
• Catalyst in black primer: Reflectance near 2020 nm detected catalyst presence at 4–14 % levels, though excess TiO2 limited quantitative precision.

Benefits and Practical Applications

NIRS enables rapid in-process decision making and final product release without reagent consumption or sample destruction. It streamlines QC workflows, reduces waste, and supports continuous monitoring of critical quality attributes such as pigment loading, moisture content, color consistency and rheology.

Future Trends and Potential Applications

Advancements in chemometric algorithms and portable NIR probes will expand in-line monitoring to complex coating formulations. Integration with process control systems and cloud-based data analytics will drive predictive quality assurance and adaptive manufacturing in paints and inks.

Conclusion

The feasibility studies demonstrate that NIRS is a versatile tool for controlling dye strength, moisture, color strength, viscosity and catalyst content in the ink and paint industry. Its speed, flexibility and non-destructive nature make it well suited for modern quality control paradigms across raw materials, process streams and finished products.