(1) Field of the Invention
This invention relates to extrusion dies for extruding thin plastic film and more particularly to an improved internal die deckle for more effectively sealing the pre-land area of the die and to reduce or eliminate edge build up as the film is being extruded. The internal die deckle differs from known die deckles in that it employs a wedge flag composed of two tapered bars which are adjustable one with respect to the other for sealing the ends of the elongated die in the film extruder.
(2) Description of the Prior Art
U.S. Pat. No. 4,454,084 issued to D. J. Smith discloses a film extruder of the general type to which the invention pertains including a die body having an internal manifold for feeding a molten polymer to an extrusion orifice defined between a pair of die jaws. Deckles at each end of the die body are adjustable within a narrow passageway or "pre-land" leading to the orifice by means of pinions and gear teeth which control longitudinal movement of each deckle to adjust the length of the die opening.
U.S. Pat. No. 3,832,120 issued to R. L. Shaffer on Aug. 27, 1974 discloses a film extruder employing both primary and secondary internal deckles. The deckles are adjustable one with respect to the other in the longitudinal direction along the pre-land area of the die. However, the deckles are not adjustable in the transverse direction for applying sealing pressure to a deckle rod.
European Patent Publication No. 0 579,142 A1 dated Jan. 19, 1994 discloses a film extruder employing an internal deckle supported by a hanging clamp assembly including a lead screw and hand wheel for longitudinally moving the deckle and a deckle plug within the area of the pre-land and manifold. However, this deckle system includes only a single deckle bar as opposed to a pair of separate bars.