Quality Control of PVC foils

Importance of the Topic

PVDC-coated PVC foils are widely used in high-performance packaging such as pharmaceutical blister packs and food packaging due to their superior barrier properties against moisture and oxygen. Accurate control of the PVDC coating thickness is essential to ensure consistent Water Vapor Transmission Rate (WVTR) and Oxygen Transmission Rate (OTR), which directly impact product stability and shelf life.

Objectives and Overview of the Study

This study aimed to establish a fast, nondestructive method for quantifying PVDC layer thickness on PVC foils using near-infrared (NIR) spectroscopy. By developing and validating a prediction model, the goal was to demonstrate the feasibility of inline quality control that can provide results within seconds and support timely adjustments during polymer production.

Used Methodology and Instrumentation

The experimental design involved measuring 250 µm PVC foils coated with PVDC layers of 40, 60, and 90 g/m2. A total of 68 spectra were recorded in transflection mode on a DS2500 Solid Analyzer. Key instrumentation and software included:

• DS2500 Solid Analyzer (Metrohm 2.922.0010)
• NIRS gold diffuse reflector, 1 mm pathlength (Metrohm 6.7420.000)
• Mini sample cups for powders and granulates (Metrohm 6.7402.030)
• Vision Air Complete spectroscopy software (Metrohm 6.6072.208)

The gold diffuse reflector ensured a constant 1 mm optical pathlength, enhancing spectral signal quality. All data acquisition and model development were performed in Vision Air Complete.

Main Results and Discussion

Using all 68 Vis-NIR spectra, a quantitative prediction model was built for PVDC thickness. Correlation diagrams showed excellent agreement between NIR predictions and reference gravimetric data. Key figures of merit included:

• Coefficient of determination (R2): 0.992
• Standard error of calibration (SEC): 1.7 g/m2
• Standard error of cross-validation (SECV): 1.9 g/m2

These metrics indicate a prediction precision better than 2 % of the nominal coating weight, confirming the robustness of the method under routine conditions.

Benefits and Practical Applications of the Method

NIR spectroscopy offers several advantages for PVDC layer thickness determination:

• No sample preparation required, enabling truly inline or at-line measurements
• Rapid analysis with results available within seconds
• Non-destructive testing, allowing 100 % inspection of production output
• High reproducibility and ease of operation in production environments

This approach can be integrated into process control systems to reduce waste, improve consistency, and ensure regulatory compliance in pharmaceutical and food packaging manufacturing.

Future Trends and Possibilities

Advances in miniaturized NIR sensors and machine learning-driven calibration models are expected to further enhance speed and accuracy. Integration with Industry 4.0 platforms will enable real-time monitoring, automated feedback loops, and predictive maintenance. Expanding the method to other multilayer film structures and adapting to mobile or handheld NIR devices will broaden its applicability across diverse packaging processes.

Conclusion

Near-infrared spectroscopy on the DS2500 Solid Analyzer successfully quantified PVDC coating thickness on PVC foils with high precision and minimal error. The rapid, non-destructive measurement technique supports real-time quality control and process optimization, making it a compelling solution for industrial packaging operations.

Reference

• AN-NIR-092, Quality Control of PVC Foils: Easy and Robust Determination of PVDC Layer Thickness, Metrohm AG