Quality Control of PVC foils

Importance of the Topic

The performance of high-barrier packaging films, such as pharmaceutical blisters and food packs, depends on the uniformity and thickness of the PVDC coating on PVC foils. Accurate control of this layer is critical to maintain low water vapor and oxygen transmission rates, ensuring product shelf life and safety.

Objectives and Study Overview

This study demonstrates a rapid, non-destructive method for quantifying PVDC layer thickness on 250 µm PVC foils. Samples with coatings of 40, 60, and 90 g/m2 were analyzed to build and validate a near-infrared (NIR) calibration model for routine quality control.

Methodology

Measurements were performed in transflection mode using a 1 mm gold diffuse reflector to maintain constant optical pathlength and enhance signal quality. Vis-NIR spectra (400–2500 nm) were collected for 68 samples without any sample preparation. Spectral data and reference thickness values were processed in Vision Air Complete for calibration and cross-validation model development.

Used Instrumentation

• DS2500 Solid Analyzer (robust NIR instrument covering 400–2500 nm)
• NIRS gold diffuse reflector, 1 mm pathlength
• Mini sample cups for film and powder handling
• Vision Air Complete software for instrument control, data management, method development, and routine analysis

Main Results and Discussion

The NIR calibration model achieved a coefficient of determination (R2) of 0.992. The standard error of calibration was 1.7 g/m2, and the standard error of cross-validation was 1.9 g/m2. Predictions differed by an average of 2% from gravimetric reference values, demonstrating excellent accuracy and reproducibility.

Benefits and Practical Applications

NIR spectroscopy enables fast, contactless measurement of PVDC thickness in seconds, supporting in-line or at-line quality control. The method reduces analysis time, eliminates consumable costs, and facilitates real-time process adjustments to maintain consistent barrier performance.

Future Trends and Opportunities

Potential developments include integration of NIR sensors into production lines for continuous monitoring, combining NIR with other spectroscopic techniques to assess multilayer structures, and applying advanced chemometric algorithms for complex material systems. Expansion to other coating materials and packaging formats can further extend the method’s industrial relevance.

Conclusion

This application note confirms that NIR spectroscopy using the DS2500 Solid Analyzer provides a rapid, accurate, and robust solution for PVDC layer thickness determination on PVC foils. The approach is well suited for quality assurance in manufacturing environments.

Reference

Application Note AN-NIR-092, Metrohm AG