Patent GB-1258744-A (GB)
IPC: B29C48/32
Filed: 1968-12-30
Abstract: 1,258,744. Textile-like sheets and films; extrusion. O-B. RASMUSSEN. 30 Dec., 1968 [28 Dec., 1967; 27 Feb., 1968; 25 June, 1968; 11 Sept., 1968], No. 61754/68. Headings B5A and B5B. A method for the production of synthetic sheet material comprises the steps of extruding separate streams of a first extrudable polymeric material and a second extrudable material, joining said streams to form a fluid sheet structure comprising lamellae of the first extrudable polymeric material in interspersed relationship with lamellae of the second extrudable, shearing out the surfaces of the fluid structure to form a sheet structure in which the lamellae are laying in flat sandwich-like arrangement and in which the lamellae of the first extrudable polymeric material are bonded together at the surfaces of the sheet structure and are substantially perpendicular to the sheet plane in the core zone, setting the sheet structure and disrupting the connections between the lamellae of the first polymeric material in the core zone and separating the sheet into two parts in a plane substantially parallel to the sheet plane either before, during or after the disruption. Extrudable first polymeric material streams may be extruded so as to form separate lamellae located on opposite sides of the plane of separation of the sheet structure and in this case the edges of the lamellae may be tapered. In this case, where the second extrudable material is also polymeric, streams of a third extrudable material may also be extruded so as to form lamellae of the third extrudable material in the plane of separation and wholly or partially removing the third extrudable material either during or after the separation of the sheet while leaving a substantial part of the second extrudable material in the sheet. The third extrudable material may be incompatible with both the first polymeric material and the second extrudable material, and the streams of the third extrudable material may be joined with the streams of the first extrudable polymeric material and the second extrudable material so as to form a continuous layer of said third extrudable material within the zone of separation of the sheet. In this way the streams of second and third extrudable materials may be joined so as to form alternating lamellae within the zone of separation of the sheet. Thus the second extrudable material may be a finely dispersed mixture of two or more polymers, whereas the third extrudable material is a substantially homogeneous material. Separation of the sheet is suitably effected by cutting action. Fig. 1 shows a sectional view of the sheet material comprising a first extrudable polymeric material forming lamellae 1 and a second extrudable material forming lamellae 2. As shown the lamellae are sheared out to form a flat sandwich-like structure near the surfaces to increase the coherence of the material in these zones while the lamellae are substantially perpendicular to the sheet plane in the core zone. The line A-A indicates the plane of separation. In Fig. 1 both surface layers consist solely of the lamellae 1 of the first extrudable polymeric material and the lamellae 2 of the second extrudable material are only present in the core zone. In the apparatus of Fig. 2, a first polymeric material 1 is extruded through the relatively long slots 8 of ring die 3 while the second extrudable material 2 is extruded through the shorter slots 9. The two parts 4 and 5 of the collecting chamber which define an extrusion slot 6 and a neck 7 are rotated together relative to the row of slots so as to exert a drag on the lamellae 1 and 2 as they are extruded from slots 8 and 9. This drag causes the lamellae to be laid in helices substantially flat along the row. Simultaneously, however, the lamellae are thrust forward by further amounts of extruded material and during this movement their edges drag against the sides of the collecting chamber and in particular against the neck 7. Thereby, the lamellae are sheared out in zones near the surfaces to form a sandwich-like arrangement as shown in Fig. 1. The extruded product consists of shorter lamellae 2 separating the lamellae 1 which consequently form the surface layers of the sheet material. If the collecting chamber (parts 4 and 5) is rotated, the equipment to haul-off the tubular sheet from the extrusion device must also rotate so as to prevent an untwisting of the helical arrangement of the lamellae. However, the collecting chamber may be in a fixed position in order to avoid such rotation of the haul-off equipment but in this case the circular row of orifices and the manifolds feeding the latter should also rotate. The slot arrangement of Fig. 2 is shown in greater detail in Fig. 3 (not reproduced) illustrating a slot arrangement comprising long slots (8) alternating with shorter slots (9) and shown rectilinearly for clarity. The slot arrangements of Figs. 4 to 7 (not reproduced) are used for the production of a sheet material having a weakened core zone thus facilitating the separation of the sheet material into two parts in a plane parallel to the sheet plane. The sheet material so prepared may be combed at the surfaces so as to bond the lamellae of the polymeric material together. The combing is carried out by means of teeth located in the collecting chamber shown in Fig. 2. In general an additional step may be used comprising combing threads out from the lamellae of said first polymeric material while subjecting the fluid sheet structures to shearing action so as to form bundles of threads bonding the lamellae together. The sheet material of Fig. 8 is prepared by separating a sheet material of the type shown in Fig. 1 into two parts by disrupting the lamella structure, e.g. by removing the lamellae of the extrudable material 2. The two parts formed are then bonded together by means of an adhesive which is applied spot-wise on to the original surface layers. By applying the adhesive spot-wise a high flexibility is obtained. The strength of the composite material may be increased by incorporating a reinforcing material, e.g. of parallel threads between the layers which are glued together, and a further increase in strength may be obtained by cross-laminating the two parts formed by the separation of the sheet material. If the surfaces of the sheet material which is to be separated in two parts have been combed so as to draw out the threads from the edges of adjacent lamellae, the lamination is preferably carried out in such a manner that in the final product the threads originally present in one of the surface layers cross threads of the surface layer which originally was opposite to the first surface layer. To increase the fineness of the pile of the sheet materials prepared so as to make such sheet materials suitable for sanitary purposes as well as for carpet applications, the lamellae may be subjected to a double drawing in the extrusion device shown diagrammatically in Fig. 9. From the extrusion slots 8 and 9 the extrudable materials 1 and 2 flow into the rotating collecting chamber 18 while being drawn through semi-fine continuous lamellae which advance through the collecting chamber almost in a broadside flow. The neck of the collecting chamber continues in a row of channels formed by the dividing walls 19, of wedge shape so that their rear ends form a series of second extrusion orifices arranged in a row. Subsequently, the material is extruded into a second collecting chamber 20 having a similar neck and continuing in a slot (21). The continuous lamellae are chopped by the walls. 19 and during the passage through the channels the flow changes from substantially a broadside flow to a substantially longitudinal flow so that the lamellae emerge in bunches from each of the channels. Each bunch is further drawn due to the movement between the walls 19 and the second extruding chamber 20 and forms a row in the extruded sheet. In slot (21) (Fig. 10, not reproduced) the chamber may widen smoothly to make the material thicker, and to raise the centre portion of the U. For this purpose the second collecting chamber may be cooled by circulation of a cooling medium through channels in its walls. The structure need not be separated before the separation step and it is possible to separate the sheet material, e.g. by cutting it in half and then if desired subjecting the separated material to a disruption step. The material of the solid lamellae of first polymeric material is normally homogeneous but this is not necessarily so. Thus the first polymeric material may be made of two components which bond strongly to one another. Alternatively, lamellae of one component may be used to form the surfaces while lamellae of the second component may be extruded to bond firmly to the lamellae of the first component and to form the core portion.