| 摘要 |
In the present invention, there is disclosed a process for preparing expanded products of polyolefins with refined structure, higher density of cells and enhanced resistance to collapse at lower temperature values of ripening, wherein the invention is characterized by extrusion of a corresponding polymeric material, wherein a liquid swelling agent is metered in the corresponding polymeric material melt during extrusion thereof. In the environmental-friendly optimized process of extruding expansion, the swelling agent, consisting of a mixture of gases containing carbon dioxide and/or at least one hydrocarbon having 3 to 6 carbon atoms, is metered into the polymeric melt at a pressure in the range of 9 to 20 MPa in two fractions, wherein the first fraction, comprised of carbon dioxide or the hydrocarbon having 3 to 6 carbon atoms is proportioned into a working cylinder at the point 1 in an amount in the range of 0.3 to 8 percent by weight, based on the weight of the mixture of the polymeric melt and swelling agents, wherein the axial distance of said point 1 from a hopper opening is 3/12 to 6/12 of the worm length, optionally length of worms, and the other fraction, comprised of at least one hydrocarbon having 3 to 6 carbon atoms in an amount of 3 to 14 percent by weight, based on the weight of the mixture of the polymeric melt and swelling agents, is proportioned in the extruder working cylinder at a point No. 2 , wherein the axial distance of said point 2 from a hopper opening is 4/12 to 8/12 of the worm length, optionally length of worms, with the proviso that the minimal axial distance of the proportioning points 1 and 2 is 1/12 of the worm length, optionally of the length of worms. |
