To prevent leaks, manufacturers of dairy product and beverage containers, packaging foils, and other multilayer packing materials need to be able to detect waving edges and temperature gaps in the plastic film during the extrusion coating process.
How can proper web temperatures for strong film-to-paper adhesion be ensured?
The packaging material for carton-based packages is composed of a laminate of paper, polyethylene and aluminium foil. Paper makes the packages stiff. Plastic renders them liquid-tight, and aluminium foil blocks out light and oxygen.
To manufacture these cartons the polyethylene feeds 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.
The internal measurement of the melt temperature by use of thermocouples in the die is not representative of the temperature distribution in the polyethylene film. With increases in the production speed (up to 700 m/min), there is an escalating need for improved quality control to ensure the integrity of beverage packing.
Infrared on-line scanning is a solution to this problem. 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.
Raytek EC100 installed on laminator to monitor glue curtain temperature profile
Surface temperature measuring of the melt curtain supplies the information about temperature distribution at the die exit. The EC100 measuring system offers a contactless temperature measurement covering the entire width of the polyethylene film. The process imager scans the melt curtain directly. For a better alignment the process imager is equipped with a line laser.
IR image showing edge defect
The 'Automatic Sector' feature of the device continuously monitors the whole melt curtain and provides automatic edge detection. The feature automatically adapts to measuring a plastic film of varying width. Temperature gaps or unacceptable 'waving' or 'edge running' are detected automatically. Within the 'Automatic Sector', temperature deviations are calculated. Unacceptable edge waving, edge running, or edge tears from one scanned temperature line to the next line are detected quickly and automatically. If a fault or defect occurs, an alarm is triggered to allow for quick corrective action.
Benefits of using this system are the automated capture of quality documentation and a reduction in scrap.
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