| 摘要 |
<p>Process for the preparation of bodies of expanded cross-linked polyethylene, with closed cells, comprising the steps of: melting a polymer of ethylene selected among ethylene homopolymers, copolymers of ethylene with alpha-olefins, copolymers of ethylene with conjugated diolefins and relevant mixtures; homogenizing the polymer of ethylene in the molten state with a quantity of from 0.1 to 2.5% by weight of a cross-linking agent and with a quantity of from 2 to 25% by weight of an expanding agent, the cross-linking agent and expanding agent having a decomposition temperature higher than the melting point of the polymer of ethylene, the homogenizing step operating at temperatures of from 130 DEG to 150 DEG C., and for times of from 5 to 10 minutes; forming the homogeneous mixture in a solid parallelepiped shape by means of extrusion and subsequent cooling, or by means of moulding wherein the extrusion or moulding step is operated at temperatures within the range of from 130 DEG to 150 DEG C. and for times of from 1 to 10 minutes; placing the solid parallelepiped shaped body inside an air-tight closed container, pressurizing the container by means of an inert gas, and heating the solid parallelepiped shaped body, at a temperature higher than the decomposition temperature of the cross-linking agent and the expanding agent contained therein, wherein this step is operated at 170 DEG -200 DEG C., under 40-70 bar for 20-45 minutes, in the absence, or substantial absence of expansion, such that expansion is limited to less than about 5%; depressurizing the container immediately following the foregoing pressurizing and heating step for a time of from 0.5 to 3 minutes, allowing the body to expand to an end volume smaller than the volume of the container, and recovering the expanded reticulated item from the container.</p> |
