Cast-film production method
Cast films may be water quenched or more generally cast onto a chilled roll. Both melts are drawn down from the die and “neck in” or narrow as they thin. These films will have a predominantly MD melt orientation, which is frozen during the quenching. Comparison of the quenching rates depends on the distance from the die lip to the quenching medium, either a water bath or a chill-roll surface.
The quenching methods are not equal in capturing and freezing the melt orientation induced in the die and the draw down. In general, it seems that the water-quenched films retain more of the melt orientation than chill-roll cast films, and that cast films will retain more MD orientation than blown films.
This is particularly apparent in uniaxially MD-oriented tapes, where water-quenched sheets yield higher-strength tapes than those formed from chill-roll quenched sheet, which is stronger than melt-blown films used for MD orientation . Tape strength also can be varied by the die-to-water surface distance at constant line speed.
2. Figure 40, Krassig, Lenz and Mark, Fiber Technology from Film to Fiber; International Fiber Science and Technology Series, Ed., M Lewin, Marcel Dekker, Inc., New York, 1984, page 79.