Abstract: An extrusion die is disclosed including a first member having a surface which includes a plurality of spiral channel segments formed therein and a second member having a surface which includes a plurality of spiral channel segments formed therein. The surfaces of the first and second members are positioned with respect to each other to form a leakage gap therebetween, wherein the spiral channel segments of the first and second members are mated to form a plurality of discrete spiral channels having spiral centerlines which serpentine back and forth across the leakage gap. A spiral channel is formed by a spiral channel segment in the first member aligned with a spiral channel segment in the second member, where the depths of the respective spiral channel segments are substantially 90.degree. out of phase.

Abstract: In a cast film process, a thin sheet of semi-molten resin is extruded from a die and directed onto a rotating cylinder such that the transverse length of the sheet and the rotational axis of the cylinder are parallel to one another. During this stage of the process, it is desired to prevent air from entering and subsequently being trapped between the film and the casting surface of the rotating cylinder. Ultimately, entrapped air results in localized film distortion and non-uniform heat dissipation from the film. The cast film process employs an air deflector to deflect this laminar air flow layer which is entrained with the surface of the rotating cylinder before it can be forced between the casting surface and the film. The elimination or substantial reduction of the tangential velocity of the entrained air layer provides more uniform adherence of the extruded film to the casting surface.