| 摘要 |
Foamed polymers are prepared by extruding at elevated temperatures a thermoplastic synthetic organic polymer and a thermally decomposable blowing agent, injecting directly into the extruder a volatile organic foaming agent to form a mixture with the polymer and blowing agent and intensively homogenizing the mixture during its passage in the direction of the die; the pressure of the mixture during said passage remaining constant or decreasing and the blowing agent being such that it decomposes in the extruder at a temperature not more than 60 DEG C. lower than the maximum mass temperature within the extruder. The polymers may be addition polymers, e.g. propylene, ethylene, vinyl chloride, or styrene polymers, suitable thermally decomposable blowing agents for the first three being azodicarbonamide, 4,41-oxy-bis-(benzene sulphone hydrazide), and diphenylsulphone - 3,31 - disulphohydrazide respectively. Suitable volatile foaming agents are the hydrocarbons having boiling points between 10 DEG and 100 DEG C. The blowing agent and the volatile foaming agent are preferably used in amounts ranging from 0.25 to 1% and from 5 to 10% by weight respectively. The extrusion may be carried out in an extruder having the ratio of its length to its internal diameter between 20 and 35, which is provided with a mixing zone wherein the foamable mass may be intensively homogenized by passing it through a number of grooved mixing elements, which are separated from each other by short, narrow, annular flow zones, thereby subjecting the mass to fluctuating tangential forces.
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