APOS UV-NIR – Online layer thickness measurement of UV rolled paints with NIR sensors

APOS UV-NIR determines the layer thickness of the coating (application quantity) after the application

UV-NIR replaces sampling and manual weighing .
UV-NIR allows to reduce variations in coating thickness and to increase plant capacity.
UV-NIR determines the coating thickness objectively, regardless of personal assessment.
Determination directly after the application on the board moving past. Values available to the second.
Non-destructive, optical process. No damaged boards and no loss. No personnel expenses.

What is APOS UV-NIR?

APOS UV-NIR is a NIR-based online system for measuring the layer thickness of a panel after coating of the UV rolled paint.
UV-NIR replaces sampling and manual of the degree of coating thickness. Interfaces to Hymmen.

Why APOS UV-NIR?

All values are automatically saved with a time stamp. Clear traceability in the event of defects in downstream production. Increase in the production seep possible. Increase the production volume without reducing quality.

Application Note: NIR Measurement of UV Curing Processes

Introduction

Near-Infrared (NIR) spectroscopy is a powerful analytical technique used in various industries for non-destructive and real-time monitoring of chemical and physical processes.
The coatings industry is faced with the challenge of ensuring the quality of its products and at the same time developing efficient analysis methods.
The UV curing process (Fig. 1 example machines) and the monitoring of the layer thickness of the coating (application quantity) after the application and the degree of conversion after UV curing play a decisive role in production.
Near-infrared spectroscopy has shown promise as a technique to address these needs. NIR enables the fast, non-destructive and comprehensive analysis of during the coating process.

Objective

The objective of this application note is to demonstrate how NIR spectroscopy can be utilized to monitor and optimize UV curing processes. By implementing this technique, manufacturers can ensure consistent product quality, improve efficiency, and reduce waste.

NIR Spectroscopy Principles

Near-infrared (NIR) spectroscopy uses the near-infrared part of the electromagnetic spectrum, which lies between visible light and infrared radiation. This technique is based on the interaction of light with chemical bonds in molecules. Each material and molecule absorbs light in a unique way, producing a characteristic signal (=spectrum). Analysis of these spectra enables substances in samples to be identified and quantified.
By measuring the absorption and reflection of NIR light, valuable information about the chemical composition, physical properties, and curing status of the wood can be obtained
NIR spectroscopy is particularly suitable for in-line and real-time monitoring due to its rapid measurement speed and non-destructive nature.

UV-coating and UV Curing Processes

The properties of the UV cured coatings depend on the quantity and the degree of conversion of the material under UV light. It is therefore important for process control to monitor this parameter.

From an economic point of view, it is important that a defined maximum amount of coating is not exceeded. In addition, the functional properties of the product depend strongly on the conversion (curing) of the coating. UV curing processes involve the use of UV light to initiate a chemical reaction in the coating applied to the material surface. This reaction leads to the crosslinking of polymers, resulting in a hardened and durable finish. Monitoring the curing process is essential to ensure proper curing time, uniformity, and avoidance of defects such as incomplete curing or overcuring.

CureKT Sensor in production of MFB Board

Experimental Setup

Hardware: APOS NIR Spectrometer System ModularNIR
Sample Preparation: Prepare representative samples (Fig. 2 examples) by applying the UV curable coating or adhesive onto substrates of known properties.
Calibration: Acquire NIR spectra of the samples (Fig 3.: measurement in process) at different amounts of coatings and stages of the UV curing process, including uncured, partially cured, and fully cured states. Simultaneously, measure reference data such as applied amount of coating, curing degree, curing time, temperature, and visual inspection.
Chemometric Analysis: Develop calibration models using chemometric techniques such as principal component analysis (PCA) and partial least squares regression (PLSR) to correlate the NIR spectra with the reference data.
Validation: Validate the calibration models using independent samples to ensure accuracy and reliability.

Data Analysis and Interpretation

Curing Degree: NIR spectra (Fig. 4) can be used to determine the curing degree by analyzing characteristic absorption bands associated with the curing reaction. A higher absorbance in these bands corresponds to a higher degree of cure.
Coating Thickness: By analyzing the reflectance spectra (Fig. 5), NIR can estimate the coating thickness, ensuring uniformity across the wood surface.
Real-time Monitoring: Develop a control algorithm that continuously measures NIR spectra during the curing process and triggers corrective actions based on predefined thresholds or models.

Conclusion

NIR spectroscopy is a valuable tool for the measurement and control of UV curing processes. By implementing this technique, wood manufacturers can enhance product quality, improve process efficiency, and reduce waste. The non-destructive nature and real-time monitoring capabilities of NIR spectroscopy make it an indispensable analytical tool for optimizing UV curing processes in the wood industry.

Benefits of NIR Measurement in UV Curing

Real-time monitoring: NIR spectroscopy enables continuous monitoring of the coating process, allowing manufacturers to detect deviations and make adjustments in real-time.
Non-destructive analysis: NIR spectroscopy does not require sample preparation or physical contact with the wood, preserving the integrity of the product.
Multi-parameter analysis: NIR spectroscopy can provide information on multiple parameters simultaneously, such as curing degree and coating thickness.
Process optimization: By analyzing NIR spectra, manufacturers can optimize curing parameters, reduce energy consumption, and minimize waste.
Quality control: NIR spectroscopy facilitates the identification of defects, such as incomplete curing or variations in coating thickness, enabling timely intervention and quality assurance.

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