HOT-MOLDED SHEET POLYPROPYLENE FOAM Russian patent published in 2003 - IPC

FIELD: polymer materials. SUBSTANCE: invention relates to manufacture of foamed sheet thermoplastics, which, in particular, serve as starting material for molding containers, vats, supports, motor car ceilings, etc. Process consists in extrusion of foaming composition comprising at least one polypropylene polymer and at least one expanding agent through die with ring-like extruding nozzle at pressure, temperature, and extrusion speed sufficient for preventing foaming of composition before it leaves die. Expanding agent is used in amount between 0.2 and 4.4 mole per 1 kg polymer. Foamed plastic is cooled to temperature below melting point of polypropylene, after which foamed plastic tube is cut radially to form sheet, in which at least 70 wt % of polypropylene has melt tension measured at 190 C within a range of 25 to 60 cN. Foamed plastic tube has density between 16 and 200 kg/cu. m, content of opened cells below 70%, circular perimeter of tube cross-section at least 1 m, and thickness of plastic between 2 and 25 mm. Method of invention enables manufacture of sheet foamed plastic, which is easy to mold on heating to acquire desired shape, configuration, or outlines. At the same time, material is sufficiently rigid to avoid whipping and preserves shape at elevated temperatures and/or when affected by direct sun light. EFFECT: improved strength characteristics, shock-absorbing capacity, sound and heat absorption. 25 cl, 1 dwg, 1 tbl, 11 ex