Patent GB-1174287-A (GB)
Title: Ribbed structures of thermoplastic resin.
IPC: B29C48/08
Filed: 1967-05-23
Abstract: 1,174,287. Ribbed films; making boxes; laminates. E. I. DU PONT DE NEMOURS & CO. 23 May, 1967 [23 May, 1966], No. 23826/67. Headings B5B, B5D and B5N. [Also in Divisions B8 and E1] A ribbed structure comprises a film and a network of ribs integrally moulded to a surface thereof and with one another, the ribbed structure being made of thermoplastic resin and having a bulk density of less than 30% of the density of the resin and the network of ribs alone having a bulk density of less than 20% of the density of the resin, especially less than 12% of the density of the resin. The ribs may form a pattern of polygonal shapes, e.g. squares as in Fig. 1, or the ribs may be parallel forming a channel structure as in Fig. 13. Suitably the film is from 0-001 to 0-025 inch thick, and especially between 0-001 and 0-005 inch thick, and the ribs of the network are spaced apart a distance which is from 20 to 50 times the thickness of the film, the cross-sectional heighttowidth ratio of the ribs being at least 5 :1. As in Fig. 2, a web made of thermoplastic resin, 18, may be laminated to the tops of the ribs, and another web of material may be laminated to at least one film 12 or 18 of the rib structure, e.g. 22 in Fig. 2. Material 22 may be plastic, metal, cloth, wood or paper, and may be applied using a suitable adhesive, e.g. applied by sprayer 24. Thus the web 22 may be metal foil and paper may be laminated to the film 18 of the rib structure and additional metal foil laminated to the paper. As in Fig. 3, a ribbed structure may be made comprising opposed rib structures laminated in rib-to-rib relationship. The ribbed structure may also be made into a container in the form of a tube or carton. Thus Figs. 4, 5 and 6 illustrate successive stages in making a box from a ribbed structure 35, which is folded and passed over anvil 41, heat sealed at 43, and the edges abutted by fingers 42, pressure finger 47 serving to confine the thickness of the seam to the thickness of the rib structure, as shown in Fig. 7. The channel structure of Fig. 13 may be similarly treated to form laminated structures, and may be used to form a heat exchanger by the use of end manifolds 156, 158 as shown in Figs. 15 to 17. In the apparatus of Fig. 8, thermoplastic resin is supplied at 52 to die 54 of extruder 50 and is extruded via passage 56 to a surface of rotating roll 58. The use of a doctor blade (not shown) serves to regulate the thickness of the base film, and the film is cooled at water spray 62, and after sufficient contact with roll 58 which is internally cooled, the web is removed by take-off rolls 64 aided by stripper roll 16 and, optionally, mould release agent applied by spray nozzles 68 to the roll surface prior to passage under die 54. Longitudinal trimming of webs 60 may be effected by one or more blades 70 prior to wind-up at 71. The die 54 is pivotally mounted about stub shaft 120, and the rod 122 and weight 124 serve to counteract pressure fluctuations at the extruder so as to maintain a constant force on the resin entering the roll pattern. Figs. 9 and 10 show two forms of casting apparatus. In Fig. 9, resin 76 passes through cavity 74 to the outlet 78 extending across the surface of roll 58, the rearward and forward edges of outlet 78 being defined by a die-plate 80 and a doctor blade 82, each adjustably spaced from roll 58. Grooves 88 and 89 mould one surface of web 60, and the opposite surface is formed by doctor blade 82 which is adjustably spaced from roll 58 to give the web thickness desired. Fig. 10 differs from Fig. 9 in that the slot-shaped outlet 7.8 includes a wedge-shaped passage 102 extending in the direction of rotation of roll 58, formed by doctor blade 82 having a slot surface 104 facing roll 58. Movement of the surface of roll 58 past opening 78 drags molten resin into passage 102 wherein the flowing resin is forced into the pattern on roll 58. This drag flow pressure created in passage 102 at the surface of the roll augments the pressure on the resin within cavity 74 of the die. Fig. 11 shows the means for laterally confining the molten thermoplastic resin as it leaves opening 78, comprising end plates 114, adjustably spaced from roll 58 by bolts 115, the end plates lying close to the shoulders 110 and having lower arcuate surfaces lying close to the corresponding surface of cylindrical ends 112. Film having only parallel ribs is obtained by using a suitably grooved roll. By heating the web sufficiently to melt the film, the film retreats or draws back into the network of ribs. Such a network may be made using the apparatus of Fig. 12, in which the web 60 is passed through feed rolls 138 and downwardly in front of hot air heater 140 which heats the air sufficiently to defilm the structure, which is thereafter quenched in water bath 148 and removed through take-off rolls 152, to form a network of ribs having no base film. Such a network can be laminated to webs as shown in Fig. 2, to form honeycomb-like structures for acoustical or structural applications. The ribs and films of the ribbed structures define closed cells which can be filled prior to closing with various media, e.g. inert gas or granular solids, or with liquids for decorative purposes. Specified materials include polystyrene, acrylonitrile-butadiene-styrene resin, polyolefins, ionomers, ethylene copolymers and blends, halogenated or per halogenated olefins, e.g. polyvinyl chloride and tetrafluorethylene polymers including hexafluoropropylene and chlorotrifluoroethylene, polyvinyl acetate and its copolymers, polymethyl methacrylate, polyamides, and their copolymers and blends, polyethylene terephthalate, polycarbonate and polyoxymethylenes. Moulding temperatures used include 200 to 250 C. for linear polyethylene; 180 to 190 C. for branched polyethylene; 200 to 250 C. for polypropylene; 240 to 280 C. for polystyrene; 150 to 170 C. for polyvinyl chloride; and 260 to 350 C. for nylon 66. Example I illustrates the production of a ribbed structure of linear polyethylene; Example II illustrates the production of a laminate from the web of Example I by adhesion to a polythene film; Example III describes the production of a ribbed structure of nylon 66; and Example IV the production of a ribbed structure having parallel ribs only from polyethylene and the production of a heat exchanger thereform. Example IV also describes the production of the panels shown in Figs. 18 to 22 from the ribbed structures of the invention.