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QUALITY ASSURANCE

PROCESS CONTROL

To control the mechanical consistency and stability of their films, Argotec utilizes thoroughly documented manufacturing procedures and equipment to standardize the extrusion process and thereby ensure consistent film quality, lot-to-lot, roll-to-roll. Three essential areas of process control are:

1. Temperature & Pressure
The variables of temperature and pressure affect the extruder's ability to pump the melted resin recipe through the die. This is true whether the process is flat-die, cast-on-carrier or blown film extrusion. These are controlled by screw speed, zone temperatures, die geometry and gap, die temperature and pressure.

2. Running Speed
The speed at which the extruder operates affects product quality. High quality films take time and energy (heat) to produce. The temptation exists for a film manufacturer to reduce operating costs by running cold and fast for higher yields and faster throughput. However, running film at low temperatures and high speeds can result in poor dimensional stability in the end-use application because the resin will tend to be oriented. Later, when exposed to ambient temperature or secondary processing heat, the polymer will attempt to relax, causing the film to change dimensions. Argotec, therefore, establishes and meticulously maintains the optimum temperature and throughput rate for consistent dimensional stability and overall film quality.

3. Measurement
Essential to any effective process control is the ability to measure critical film properties and adjust extrusion operation parameters accordingly to ensure consistently high product quality and adherence to customer specifications. Argotec utilizes highly accurate measurement systems to maintain consistent sheet thickness. These systems include microprocessors that continuously record film thickness. Repeatedly comparing that result against the customer's specification allows the flat-die-extruder operator, when possible, to make needed in-process adjustments in the die gap to thereby maintain the predetermined gauge standard.

While Argotec uses sophisticated measurement systems on both its flat-die and blown-film extruders to track any gauge variation, in-process adjustment of the die is possible only on flat-die extruders. This capability allows the operator to correct any variations in thickness as soon as they are detected, yielding a flat roll put-up.

Conversely, while Argotec measures bubble thickness during blown-film extrusion, in-process adjustments are not possible because this process utilizes a rotating circular die. Should a variation in film gauge occur, however, the rotation of the die will spread the disparity across the entire width of the finished sheet, resulting in the flattest possible roll put-up. (See diagrams below comparing distribution of gauge variations between flat-die and blown-film extrusion.)

The diagrams above compare the difference in gauge variation coming off flat and circular dies, and how, if left uncorrected, they can effect final film roll put-up. However, gauge variations in flat-die-extruded film can be corrected in-process by the machine operator adjusting the die gap; gauge variation in blown film cannot be corrected in-process, although it is typically spread evenly across the width of the roll by the rotation of thecircular die.