GB779646A - Extrusion dies for use in the continuous manufacture of films - Google Patents

Abstract

<PICT:0779646/IV(a)/1> <PICT:0779646/IV(a)/2> <PICT:0779646/IV(a)/3> <PICT:0779646/IV(a)/4> <PICT:0779646/IV(a)/5> An apparatus for extruding films with beaded edges includes an extrusion die which comprises (1) two blocks having outer slanting lower portions whose inner surfaces form extrusion orifice lips, one of the blocks having an inner chamber for the liquid to be extruded and the other block having an inner surface which is smooth except for two bead-forming spaced grooves which terminate near the ends of the orifice in slots of similar cross-section; (ii) a spacer plate serving to separate the blocks and having a cut-away portion similar in size and shape to the inner chamber, and bearing an orifice bar near its outlet, the plate defining an elongated slot orifice in conjunction with the inner surfaces of the blocks; (iii) means for holding the blocks and plate together; and (iv) a passage in the first block for the introduction of a liquid into the chamber. A preferred form of die is shown separated into its parts in Fig. 2 and in crosssection (assembled) in Fig. 4. The die consists of two blocks 14, 15 which are bolted together with the interposition of a spacer plate 16, whose thickness determines the thickness of the extruded film. Block 14 has a conduit 12 through which the material passes into a recess 18 with sloping bottom wall 19. Uniform distribution of the material is assisted by bar 17, which is removably located by lugs 22 in spacer plate 16 (see also Fig. 5) and which is tapered upwardly and downwardly on the side which faces the block 14 and is also tapered from its centre towards its sides. Spacer plate 16 has an aperture 20 corrsponding in shape to the recess 18 in die block 14, and has sloping portions 23 adjacent to the opening to provide a larger flow of material at these positions, to assist formation of the beads. The width d of the aperture determines the width of the film as extruded. Die block 15, which is shown in perspective from below in Fig. 3, has two slots 24, which also permit an increased flow of material to form the beads. The aperture of the slots is adjustable by a pair of plates 29 carried by a transverse bar 28 slidably arranged in slots 26 in the die block 15. The die may be made of stainless steel, alloy steels such as vanadium steel, brass, bronze, titanium or titanium alloy. The spacer plate 16 may be of steel, titanium, copper or aluminium. The assembled die is disposed with its aperture slightly above a casting drum (see Fig. 1) and the peripheral speed of the drum 10 is faster than the rate of extrusion. A bead-forming roller 36 is located near the extrusion die and presses against the film on the drum. Materials which may be extruded are synthetic resins and superpolymers such as polyethylene terephthalate, nylon, polyethylene, polystyrene, polyvinyl halides, polyvinyl acetate, rubber hydrochloride, cellulose derivatives, polyesters from glycols and aliphatic dibasic acids and polyesteramides. Specifications 578,079, [Group IV], 617,129 and 746,386 also are referred to.