| 摘要 |
1338291 Making foamed sheets MONSANTO CHEMICALS Ltd 16 Feb 1972 [16 March 1971] 6957/71 Addition to 1264852 Heading B5A A foamed sheet is produced by extruding foamable thermoplastic resin through a die slit 1 into sliding contact with a first roller 5 having its axis parallel to the slit so that as the resin foams its expansion is restricted in a direction parallel to the slit by the frictional contact with the first roller, and passing the resulting foamed sheet 9 through the gap between the roller 5 and a second roller 7. The first roller 5 is stationary or driven in same direction as, but slower or faster than, the resin. The resin may also be in sliding contact with roller 7 or this roller may be an idler. The sheet is cooled by contact with part of the circumference of the rollers 5, 7 which are cooled internally with air or water, or externally by air jets 8. An air knife (not shown) may cool the resin sheet. The sheet is hauled off at a higher speed than it is extruded to reduce sideways expansion, using a roller nip or a co-operating tracks. A glass or matt surface may be imparted by a three roll calender or the sheet may be vacuum or pressure formed, and embossed or laminated to paper, fabric or film. The die is mounted on a screw extruder (not shown) which is heated electrically and cooled by water in coiled tubes fitted in grooves around the barrel. The die body, side plates and lips are separately heated by pressurized steam. Wall and ceiling panels, containers, and body panels and shells of cars, boats and furniture are formed from homo-polymers and co-polymers of olefins, vinyl and vinylidene monomers, and acrylates, including A.B.S. Nucleating agents are included in the resin and blowing agents comprising compressed gases, volatile liquids and decomposable solids are injected under pressure into the melt in the extruder. |
