Real-Time Measurement of the Temperature Profile Across Hot Plastic Film by High Speed IR Line-Scanning Provides Feasible Means for On-Line Control of Extrudate Web Temperature

Abstract

Summary The entire process of coating paper substrate in wrapping materials hinges upon the temperature of the hot plastic extrudate, with only a very narrow tolerable temperature range. Recent tests with high-speed, narrow-bandwidth IR line-scanning on the molten plastic sheet, just under the extrusion die, have provided realtime electronic analog signals of the temperature profile across the entire web. Manual adjustment of the extruder's temperature regulators was undertaken by observing an oscilloscope display of this temperature profile analog signal only. The result was that correct adjustment of the temperature across the web was achieved - as confirmed by off-line laboratory tests for amount of film oxidation and quality of adhesion of the film to the substrate. The technique offers a practical means of obtaining on-line electronic signals for comparing with settable never-exceed temperature level voltages to provide Go/No-Go indications and automatic fail-safe process-shutdown functions. And it promises to provide a feasible means of getting at the problem of automatic proportional control of the extrudate temperature by connecting the IR line-scanner to a process control computer.