GB1231144A - - Google Patents

Abstract

1,231,144. Die for extruding films having zones differing in thickness; laminates. INTERNATIONAL PAPER CO. 16 Jan., 1969 [26 Jan., 1968], No. 2633/69. Headings B5B and B5N. As shown in Fig. 3, a die for melt extruding a film of thermoplastic material having predetermined zones differing from one another in thickness comprises a die body 18 (Fig. 3) comprised of two mated die parts or halves 21 and 22 provided with heating elements 23 and 24. The lower part of the die body is formed of opposable jaws 25 and 26 each having flat, parallel, internal surfaces which define lands 27 and 28 respectively defining a slot-shaped extrusion orifice 29 through which the thermoplastic material is extruded in the form of a molten flat film 30 (Fig. 2). Header 17 is a central cavity which extends the length of the die body 18 and communicates with an extrusion opening 31 the other end of which communicates with the extrusion orifice 29. The cross-sectional area of the extrusion opening 31 is greater than the cross-sectional area of the orifice 29. Each of the wall elements 32 and 33 of the opening 31 are provided with a longitudinally extending recess or groove of semicircular cross-section 34 and 35 defining a channel 36 of circular crosssection. The channel 36 accommodates a cylindrical flow regulating rod 37 divided into two or more threaded segments of the same outer diameter, each segment having threads of different depth, as shown in Fig. 4 illustrating a rod having three segments. As the molten plastic, after passing down the slot 31, passes between the various segments of the rod 37 and the walls of the channel 36, a profile of varying thickness is imparted to the film 30 by the various threaded segments, and as the profiled film flows past the threaded rod 37 and then down and through the orifice 29 the film retains this profile of varying thickness. After passing through a draw-down zone or air gap 38 (Fig. 2) the still molten film 30 contacts preselected areas of an advancing web of substrate material 39, which is carried on a clockwise rotating pressure roll 40, just prior to reaching nip 41, between pressure roll 40 and chill roll 42, whereby the substrate is coated with a solidified film of the thermoplastic material. The substrate 39 is preferably paperboard, but may be paper, glassine, regenerated cellulose film, polymeric films such as poleyster films, metal foil, cloth, or glass fibre cloth. The thermoplastic material used can be polyolefines, polystyrene, polyvinyl chloride, polyurethane, polymethyl methacrylate or nylon. Polyethylene is preferred.