Patent GB-1305826-A (GB)
IPC: B29C48/10
Filed: 1970-05-08
Abstract: 1305826 Partially oriented laminated films; extruding multi-layered sheets MULTIFOL PATENTVERWERTUNGS AG 8 May 1970 [9 May 1969] 22366/70 Headings B5A and B5B In a process for making a partially oriented multi-layer plastic film or sheet a plurality of plastic layers are led to meet in an extrusion head adapted for the extrusion of laminated films or sheets, and then immediately subjected to an orienting treatment, the process comprising co-extruding at least three layers of thermoplasticized polymeric material, the middle layer having a relatively high melting temperature, and the two outer layers having a relatively low melting temperature, leading the joined layers during a predetermined period of time through a cooling passageway of annular crosssection, said outer layers being in contact with the inner and outer walls of said cooling passageway, said predetermined period of time and the cooling action of said cooling passageway being such as to cool down the middle layer below its melting temperature, but, however, to maintain the outer layers of the joined layers above their melting temperature when arriving at the outlet of said cooling passageway, and stretching the extruded laminated film or sheet in the longitudinal and/or the transverse direction, so as to orient said middle layer, the friction between the outer layers of the joined layers in said cooling passageway and the walls of the passageway being sufficient so as to prevent the joined layers as appearing at the outlet of the cooling passageway from being torn from the joined layers as appearing in a section upwards of said outlet, in which latter section all layers are still in a condition above their melting temperatures.  The extruded laminated film or sheet may be stretched in the extrusion direction; the film may however be extruded as a laminated tubular film or sheet which is then stretched transversely by inflation. In either case the effect of the stretching is to orient the solidified middle layer while the outer layers being still molten, do not become oriented on stretching. The middle layer of the laminated film may be a polyamide layer and the outer layers may be polyolefin layers or ionomer resin layers. The polyolefin may be a terpolymer of ethylene acrylic acid, and an ester of acrylic acid such as methyl or ethyl acrylate. As shown in Fig. 1, an extrusion head 10 adapted for the extrusion of tubular three layer laminated films according to the invention is provided with three passageways 12, 14 and 16 of annular cross-section. Passageways 12 and 16 are fed with molten polyethylene from screw extruders 20 and 28 respectively, while simultaneously passageway 14 is fed with molten polyamide from screw extruder 24. At 30 the three passageways 12, 14 and 16 converge and open into a main passageway 32 of annular cross-section. An extension 34 is attached to the extrusion head 10 but separated therefrom by a layer of insulation 36. A cooling passageway 38 within the head extension 34 constitutes a continuation of the passageway. 32 and is cooled by coolant ducts 40, 42 and 44 of annular cross-section. The coolant duct 40 cools the inner wall of the cooling passageway 38 and communicates through lines 54, 56 extending through the core of the extrusion head 10 with a coolant source. The cooling passageway 38 is cooled from the outside by the coolant ducts 42, 44 communicating through coolant lines 46, 48 and 50, 52 respectively with a coolant source. The tubular laminated film extruded from the extrusion head 10 is stretched longitudinally by a pair of draw rolls and transversely by inflation in the usual manner.