Temperature Measurement


Extrusion coating: how can proper web temperatures for strong film-to-paper adhesion be assured?

August 2008 Temperature Measurement

Manufacturing of beverage containers, packaging foils, and other multilayer packing materials all have a common problem, that of detecting waving edges and temperature gaps in plastic film during the extrusion coating process.

Carton based packages are composed of a laminate of paper, polyethylene and aluminium foil. The paper provides rigidity, plastic renders them liquid-tight and the aluminium foil blocks out light and oxygen.

During the manufacturing process, the polyethylene is fed through several extruders at temperatures of up to 320°C. The melt is fed over a wide slot die and laminated onto the paper.

Temperature and viscosity variations in the local melt streams across the width of an extruder flow channel can cause waving edges, gaps, and edge-tears in the extruded film. In practice a 10°C temperature difference influences adhesion between the polyethylene layer and the paper and the polyethylene film can tear off when feeding from the extruder die.

With increased production speeds (up to 700 m/min), there is an increasing need for improved quality control to ensure the integrity of the packaging material, particularly in the beverage industry. The solution is simple, infrared on-line scanning.

The EC100 system from Raytek is an automated surface inspection system for detecting, measuring, and classifying defects occurring in extrusion coating, co-extrusion and laminating processes.

Surface temperature measuring of the melt curtain supplies the information about available temperature distribution at the die exit. The EC100 measuring system offers a contact-less temperature measurement covering the entire width of the polyethylene film. The process imager scans the melt curtain directly and for better alignment the process imager is equipped with a line laser.

The Automatic Sector feature, unique to EC100, continuously monitors the whole melt curtain and provides automatic edge detection. Temperature gaps or unacceptable waving or edge running are detected automatically.

Automatic sector functionality calculates temperature deviations, allowing unacceptable edge waving, edge running, or edge tears from one scanned temperature line to the next to be detected quickly and automatically. If a fault or defect occurs, an alarm is triggered allowing quick corrective action to be taken. Benefits include:

* Waving edges and temperature gaps are detected automatically.

* Optimum temperature control for strong film-to-paper adhesion.

* Improved process control and increased throughput.



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