Patent GB-1479335-A (GB)
Title: Process and apparatus for extruding filled plastics compositions
IPC: B29C48/12
Filed: 1974-11-20
Abstract: 1479335 Extruding filled thermoplastics MITSUBISHI PETROCHEMICAL CO Ltd 20 Nov 1974 [27 Nov 1973 29 Nov 1973] 50376/74 Heading B5A A section comprising thermoplastic resin and filler material is extruded from a die 4, Fig. 2, having cooling means at its downstream end which solidifies at least an external layer of the section prior to its issue from the die, and comprising passages 12 or 15 through which cooling medium is circulated at a temperature and flow rate which are independently controllable. Heating means, e.g. band heaters 17, are provided at the upstream end of the die. To minimize torsional stress, and consequent twisting of the section, arising from the torque of the extrusion screw 7, the material is delivered to the die through a channel 10 which is either narrowed by constriction as shown, or by opposed projecting bolts, to less than 0À8 of the area of a following part of the channel. The extrusion passage is preferably lined, or coated, with PTFE and is preferably more than 10 cm. long, e.g. more than 30 cm., and is preferably above 20 times the maximum thickness of the section. The coating medium may comprise water, air, or oil. A larger number of the passages 12 or 15 are arranged adjacent thicker parts of the section and the passages may differ in diameter, to further minimize twisting and longitudinal warping arising from differing flow rates of the material through the die across the section. Twisting and longitudinal warping of the section are also minimized by passage of the section issuing from the die, between a plurality of adjustably spaced apart roller pairs 19a and 19b, &c., as the section is reheated by infra-red heaters to a temperature of between 50 C. and the solidifying point of the resin, and preferably to 30 C. therebelow. The roller pairs may be aligned to give a convex curvature to the thicker side of the section, having a tendency to warp in the opposite curvature. The extruded section may comprise a door threshold, or a sash, in respect of which the Figs. 8 and 9 sections (not shown) are specifically referred to. The extruded section may be of the L-section extruded from the Fig. 3 die, or a T- or H-section, or of a channel section having inturned flanges and a base having a pair of longitudinal grooves, Figs. 4, 9 and 8 (not shown). The resin may comprise polyvinyl chloride, polyamide, A-B-S co-polymer high density polyethylene, or polypropylene, or various specified olefin co-polymers. The filler is present in 10-80%, and preferably 20-70% by weight, and may comprise an organic filler such as wood powder, bagasse or chaf, and/or an inorganic filler such as Al(OH) 3 , talc, clay, and calcium carbonate. The material is fed to the extruder as a powder or pellets, having less than 2% volatile matter. The examples relate to the extrusion specified weight preparations of: (1), polypropylene and wood powder; (2), a graft co-polymer of polypropylene with maleic anhydride, polypropylene, wood powder, and calcium carbonate, extruded to the Fig. 8 section. Physical and thermal expansion properties of the extruded section are stated.