Patent GB-1330047-A (GB)
Title: Method of extruding a hot melt
IPC: B29C48/91
Filed: 1971-07-01
Abstract: 1330047 Extruding petroleum wax composition MOBIL OIL CORP 1 July 1971 [1 July 1970] 30888/71 Heading B5A [Also in Divisions B1-2 C3 C5 and H5] A hot melt composition, for application as moisture and heat sealable coatings to paper and cardboard, and containing at least 40% by weight of petroleum wax, is formed into particles suitable for feeding to the melting reservoir of the coating machine by mixing the materials of the composition in a molten condition in which it is extruded through an electric resistance heated nozzle, of circular, semi-circular, triangular, rectangular, or polygonal section, to pass through a pair of sequential water cooling baths in which it is respectively cooled to form a solidified skin by water, at a temperature of 20 C. to 60 C. and below the melting range of the composition, and then solidified throughout by water at a temperature of 10 C. to 30 C. and below that of the first bath. The hot melt composition may be based on specified compositions (see Divisions C3 and C5), including numerous specified thermoplastics. A plurality of extrusion nozzles is preferably provided from which, at high extrusion and cooling bath temperatures, the extrudate may break into short lengths within the first bath and float to the top thereof from which it may be conveyed to the second bath by e.g. a star paddle or belt. The composition may be laterally, or vertically downwardly extruded into the bath, but in the preferred embodiment the molten composition is supplied, via a steam jacketed manifold 22, for extrusion vertically upwardly from nozzles 25, at the base of the first cooling bath 28 from which it is passed, as continuous strands e.g. by corrugated rubber rolls, over a weir 30, and through the second bath 31 from which the strands are delivered, by a star paddle 32 and through rolls 33, to a chopper 34, from which the granules are delivered by a conveyer belt 35 to a conveyer belt 37 beneath hot air drier hoods 36, and thence by a belt 38 to a packing station 39. Instead of the star paddle 32, a conveyer belt may be employed on which the strands are dried by an air blast. The temperature of bath 28 may be controlled by heating or cooling coils, or by the addition of colder water with baffles being provided at the inlet thereof to avoid displacement of the strands. The hot melt composition is supplied to the nozzles 25 by a gear pump 24, from a steam jacketed blending kettle 13 provided with outer and inner paddles driven by motors 18, 19, and which kettle 13 is supplied with the composition melted, e.g. under nitrogen or carbon dioxide, in a container 10 containing a steam heated coil 12, via a gear pump 16 and a meter 17 monitoring the feed rate. The kettle 13 is provided with a circulating loop including a pump 21. The extrusion nozzles 25 are of stainless steel and are heated by the direct passage of a D.C. or A.C. current along the relatively small crosssection wall of a conduit 52 defining the extrusion passage, the current being passed by a voltage applied between the metal tank of the water container, to the base 27 whereof the nozzles 25 are mounted, and an outer annular portion 53 of the nozzle which is connected to a terminal 61, via a metal plate 54, strap 56 and a stud 58 which passes through the tank wall 59 at an insulating bushing 60. The nozzle portion 53 is connected e.g. integrally or by welding, to the outlet of the conduit 52 and is otherwise insulated from the remainder of the nozzle by a collar 55 e.g. of phenol-formaldehyde or furfural resin, ceramic, or mica, which may as shown be extended as a sleeve between the portion 53 and conduit 52. Heating currents of 30 to 130 amps., and preferably 90-110 amps. to 1 volt are used, applied by a step down transformer e.g. 200:1 for 200 V. supply, fed by a three junction silicon controlled rectifier whose D.C. gate voltage is manually controlled by a variable resistance. To avoid heat losses, the extrusion outlet of conduit 52 may be substantially flush with the plate 54, the portion 53 may be of a greater thickness to ensure that it is heated less by the current, or the nozzle may be heat insulated by a surrounding plastics, mica, or ceramic collar.