Patent GB-1140068-A (GB)
Title: A method and apparatus for the production of multilayer articles
Inventor: CHISHOLM DOUGLAS STEWART
IPC: D01D5/28
Filed: 1966-01-21
Abstract: 1,140,068. Multilayer films and sheets; extrusion dies. DOW CHEMICAL CO. 21 Jan., 1966, No. 2932/66. Headings B5A and B5B. A method of producing multilayer composite thermoplastic resinous shaped articles, e.g. films and filaments, is characterized in that separate diverse streams of thermoplastic resinous materials in heat plastified form are combined into a single main stream, thus providing a composite stream of said materials in heat plastified form, deforming said main stream to provide a second stream of heat plastified thermoplastic resinous material, containing a number of layers of diverse thermoplastic resinous material in a heat-plastified form greater than the number of layers in the composite stream and forming the stream into a desired configuration having at least one major surface wherein the layers of the stream lie generally parallel to the major surface thereof, and subsequently cooling the composite resulting material to a temperature below the thermoplastic temperature. Fig. 1 shows diagrammatically a suitable apparatus 10 which comprises first and second sources of heat plastified thermoplastic resinous material 11, 12, and optionally, a third such source 13, a combining means 15 adapted to arrange the heat plastified material in adjacent lavered relationship in a stream, a layer multiplying means 16 wherein the stream of material is physically re-arranged to provide at least an apparent increase in the number of layers, and a shaping die 17 so constructed as to permit substantially streamline flow and to shape the stream to a desired configuration. Reference numeral 18 indicates a layered product so prepared. One form of such apparatus is shown in Figs. 2 to 5. Heat plastified thermoplastic resinous material comprising polymers A, B and C is supplied to the chambers 34, 40 and 44. From chamber 44 polymer A is extruded as a plurality of strips from the apertures designated A (see Fig. 5), polymers B and C emerging likewise from the apertures B and C. Thus the sequence of layers or strips is ABC, ABC, ABC, ... entering opening 51 of transition piece 55. As this layered stream passes through passageway 56 of transition piece 55, the width is decreased and thickness increased until the stream acquires an essentially square cross-section at exit 58. The stream portions maintain their relative location to one another and no rotation of the flow lamina occurs. On passing through the stream multiplying section 60, the stream is divided and recombined to provide a stream entering passageway 77 of transition piece 75 having about four times the number of layers that entered the stream multiplying section. Transition piece 75 reshapes the essentially square stream emerging from section 60 to expand the stream in a direction parallel to the major surfaces of the layers in the stream, and the stream is finally extruded through sheeting die 85 as a thin sheet of film. The number of layers is readily increased by increasing the number of stream multiplying sections such as 61 and 62. The operation of the stream dividing and recombining means is described in British Specification 900,656. Fig. 6 shows an alternative embodiment. In this apparatus, polymer A enters passageway 112, flows in and about the annular chamber 109, through passages 115 of the feed block 114 (Fig. 6A) and into annular orifice 130. Polymer B from source 102 flows through passage 124 into annular chamber 122, through passages 119, into the radially extending slots 118 and into annular passageway 130. Polymer C from source 103 flows through passageway 127 into annular chamber 125 and thence into the radially disposed slots 116 and into annular passageway 130. Employing the feed port arrangement of Fig. 6A the stream flowing in the annular passageway 130 adjacent the feed port comprises a plurality of radially extending layers composed of polymers ABC, ABC, ABC. On entering the portion of the annular passageway 130 defined by the die portion 136 of the mandrel 135 and the external die portion 160, the various radially extending layers are transformed into spirally disposed layers when a difference in rotational speed exists between 135 and 160. Advantageously, 160 and 135 are rotated in opposite directions in order to achieve a maximum spiral for a minimal residence time within the annular passageway 130. The product discharged at extrusion orifice 169 comprises a multilayer tube having a plurality of spirally disposed components extending from the inner surface to the outer surface, the spiral configuration being determined by the linear rate of travel of material through the rotating portion of passageway 130 and the rates of rotation of the external die portion 160 and mandrel 135. Fig. 6B shows an alternative arrangement of a feed block 114<SP>1</SP> designed to produce a tube having spirally arranged layers of the sequence ABCB, ABCB, ABCB .... This is advantageous where the B layer either promotes or prevents adhesion of the A and C layers, whichever phenomenon is desired. Fig. 6C shows an alternative arrangement of a distribution ring 114<SP>11</SP>, shown in section in Fig. 6D. The resultant product is schematically illustrated in Fig. 6E and comprises a tube having an outer layer 181 composed of polymer B containing helically oriented filaments 182 of polymer A and an inner layer 183 of polymer C containing helically oriented filaments of polymer A. This configuration is achieved when the guide portion 160 and mandrel 135 are rotated in opposite directions. Fig. 6F shows an alternative crosssection of a distribution block 114<SP>111</SP>, which arrangement results in the encapsulation of a polymer B entering passageway 119<SP>111</SP> and being discharged from slot 118<SP>111</SP>. Fig. 7 shows a modification of the apparatus of Fig. 6. Cavities 197, 198, 199 receive polymers A, B, and C, respectively, from sources 201, 202 and 203. Distribution block 196 discharges polymeric layers into a generally annular passageway 199 in a manner identical to that of block 114 of Fig. 6. Fig. 8A shows a schematic crosssectional view of a sheet produced by the apparatus of Fig. 7, comprising a plurality of layers of polymer 221, 222 and 223 in an elongated spiral configuration. Fig. 9 shows an alternative embodiment of the invention employing feed streams essentially as obtainable from Fig. 6 and the various feed ports of Figs. 6B, 6C, 6D and 6F. In operation, striated or layered feed stream from passageway 231 passes through the generally conical passageway 244 wherein the striations are spirally disposed. The material contacts the rod 246 which is withdrawn, thus providing a multilayer coating thereon. If rod 246 is omitted a rod or filament having a spiral laminated configuration is made. An alternative modification of this apparatus is to employ a solid mandrel and extrude a rod having spiral layers of laminations. Fig. 10 shows a schematic cross-sectional view of an elongated article such as the article 246 having a multilayer spirally laminated coating 247 on the external surface thereof. Fig. 11 shows a fractional end view of a structure prepared by the apparatus of Fig. 1 and the various embodiments described, which comprises an iridescent film 251 comprised of a plurality of layers 253 of a transparent synthetic thermoplastic resinous material which lie between and adhere to a plurality of layers 254 of another transparent synthetic resinous material, a transparent surface layer 255 being adhered to an adjacent layer 253. The refractive indices of the thermoplastic resinous materials comprising layers 253 and 254 differ by at least 0À03. A pressure-sensitive adhesive layer 257 is disposed in contact with the film 251 remote from the surface 255, and secures the film to a substrate 258. Further particulars of methods of making composite iridescent film structures are given below. Fig. 12 shows schematically a fractional view of a portion of a composite foamed sheet 310 which comprises first and second outer unfoamed skins 312 and 313, a plurality of unfoamed layers 314 disposed in generally parallel relationship to each other, and a plurality of foamed or expanded layers 316, separated from adjacent layers 316 by means of the unfoamed layers 314. Each of the layers is bonded to the adjacent layers. A foamed sheet as shown is readily made by means of an apparatus as shown in Fig. 13. Said apparatus comprises in combination first and second extruders 321, 322, one extruder being adapted to deliver a non-expandable thermoplastic resinous material in heat plastified form and the remaining extruder being adapted to deliver an expandable thermoplastic resinous material in heat plastified form. A distributer 323 receives heat plastified streams from extruders 321 and 322 via conduits 325 and 326. Distributer 323 has a discharge opening 328 in operative communication with a stream shaping or transition section 327 having a first opening generally commensurate with the opening 328 of distributer 323. Remote from opening 328 is a discharge opening 329 which has a major axis disposed at about right-angles to the major axis of opening 328. Transition piece 327 is constructed in a generally tetrahedral configuration which permits streamline flow of the heat plastified thermoplastic resinous material therein without rotation of the flow lamina. Issuing from opening 329 is a laminated sheet 330 substantially similar to sheet 310 of Fig. 12. Fig. 14 shows the internal configuration of distributer 323. By using the various modifications of the basic principal operation of producing a striped sheet, i.e. a sheet comprising diverse thermoplastic resinous materials, in laterally discontinuous relationship to each other, and subjecting the sheet (and including tubes which for purposes of the invention, may be considered as sheets bent into a cylindrical configuration) to lateral def