Evaluation of Concentration of Coarse Particles in Paints

Significance of the Topic

Coarse particles and aggregates in paint and ink formulations can lead to equipment blockages, surface defects, and inconsistent coatings. Monitoring their concentration in production and quality control is essential to maintain product performance and prevent operational issues.

Objectives and Study Overview

This study aimed to evaluate the concentration and size distribution of coarse particles in commercial fountain pen inks without extensive dilution steps. Using the iSpect DIA-10 system, black, blue black, and red inks were analyzed to demonstrate rapid detection and quantification of micron-scale impurities.

Methodology and Instrumentation

The dynamic particle image analysis method employs a telecentric optical system to capture high-resolution images of particles flowing through a microcell.
Key measurement settings:

• Particle size range: 5–100 μm
• Frame rate: 8 frames per second
• Pump rate: 0.1 mL/min, volume per measurement: 500 μL
• Dilution rates: black ink 20×, blue black ink 6×, red ink undiluted
• Image threshold and brightness adjusted for each ink color (average brightness 80–90, threshold 60–68)

Used Instrumentation

Shimadzu iSpect™ DIA-10 Dynamic Particle Image Analysis System with:

• Telecentric optical design ensuring minimal particle loss and high image acquisition efficiency (>90%)
• Microcell flow chamber allowing direct analysis of high-concentration or turbid samples with low or no dilution

Main Results and Discussion

• Black and red inks contained numerous particles below 10 μm, with detectable peaks around 50 μm.
• Blue black ink showed a dominant peak under 10 μm and a broad distribution extending to several tens of micrometers, with the highest overall particle count.
• Particle images revealed varied morphologies (amorphous, elongated), enabling inference of foreign matter, aggregates, or large primary particles based on shape and brightness.
• Calculated undiluted concentrations: black ~1.2×10³ counts/mL, blue black ~2.9×10⁵ counts/mL, red ~2.2×10² counts/mL.

Benefits and Practical Applications

• Rapid, high-throughput detection of coarse particles improves quality control workflows.
• Minimal sample preparation and low dilution preserve sample integrity and reduce analysis time.
• Direct analysis of colored or turbid samples without interference from background color.
• Quantitative concentration data serve as a reliable indicator for process monitoring and batch release decisions.

Future Trends and Potential Uses

• Integration with real-time process analytical technology (PAT) for continuous monitoring in ink and paint production.
• Expansion to automated classification using machine learning for detailed particle characterization.
• Combination with complementary methods (e.g., dynamic light scattering) to extend detection to submicron ranges.
• Application in broader industries such as pharmaceuticals, food, and cosmetics for impurity analysis.

Conclusion

The iSpect DIA-10 system enables precise, efficient evaluation of coarse particle concentrations in fountain pen inks with minimal dilution. Its high detection efficiency and ability to analyze colored samples make it a valuable tool for industrial quality control, helping to identify and prevent defect-causing contaminants.