| 摘要 |
1470267 Extruding longitudinally oriented foamed sections SOC CHIMIQUE DES CHARBONNAGES 3 June 1975 [5 June 1974] 23958/75 Heading B5A [Also in Division C3] A foamed thermoplastics section, having a ratio of density to that of the unfoamed material of 0À4 to 0À9, and which is oriented and has cells which are elongate, in the direction of the longitudinal axis of the section, is produced by extruding the thermoplastics containing the blowing agent at a temperature corresponding to the "rubbery flow" region, D, Fig. 1, cooling the extrudate around its periphery immediately at the outlet of the die and to a temperature of the "rubbery plateau", C, and drawing it through a metallic sizing die and a following cooling zone, with the extrusion and sizing die passages corresponding in shape and size to that of the section, and the ratio of extrusion speed to that at which the section is drawn from the sizing die corresponding to the density ratio of the section. The process requires an elongation of the order of 100% of the surface regions of the extrudate, obtained by the cooling to a temperature of the "rubbery plateau" of the material. For density ratios of 0À4 to 0À6, the temperature of the remainder of the extrudate may be that of the rubbery flow region, D. The peripheral cooling is preferably effected by jets of cold fluid directed at pressures which may be constant around the periphery in the case of a circular section rod, or may vary around the periphery, as in Specification 1,450,990, for sections such as that of the example, Fig. 2, where a specified foamable polystyrene homopolymer composition is extruded from the die P, and cooled by jets 1-7. The thermoplastics may also comprise polyvinyl chloride or polystyrene, or copolymers comprising one thereof. |
