| 摘要 |
<PICT:0876549/III/1> Thermoplastic coatings (e.g. polyethylene, nylon) are applied to the interior surfaces of tubular articles, e.g. of metal, cellulose or synthetic resin, by injecting a gas into a bubble of the molten thermoplastic material while it is being extruded, the bubble being positioned within the article to be coated which is moved in the direction of flow as the article receives the extruded blown melt from the extruder. In an illustrated example, thermoplastic material is moved through the passage 8 by the action of the extruder 1, thence through the annular die 7. Spacers 6, placed at intervals along the tube 5, separate it from the pipe 11 to be coated. Extrudate is released through the die 7 in the form of a hollow tube which is sealed by pinching. Air is then introduced via an air line 4 positioned lengthwise along the tube 5 and directed to a bore in the spider 12. The pipe 11 is moved in the direction of the extrudate flow and the extrudate is forced against the inner wall of the pipe 11 by the injected air. When the coating is completed, the extrudate is pinched off on the forward side of the die, to allow formation of a bubble in preparation for repetition of the process. The coating material may contain fillers, e.g. titania, carbon and colloidal silica, and additives such as fumaric acid, and they may be treated with cross-linking agents, e.g. high speed eletrons, or organic peroxides, after application. Metal surfaces may be primed with adhesion-promoting primers, e.g. those based on polyisocyanates. Specification 778,034 and U.S.A. Specifications 2,695,255, 2,803,056 and 2,838,437 are referred to.
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