Process for foaming flame retardant polystyrene and polystyrene shaped articles
AssigneeHoechst Aktiengesellschaft
InventorsHub A. G. Vonken, Jan op den Buysch
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Abstract
Polystyrene melts treated with flameproofing agents and nucleating agents are foamed by addition of alkanes, such as propane, butane or propane/butane mixtures, as blowing agents, such that the flame retardant properties of the polystyrene foams are achieved after a very short storage time, or at the latest after storage for three weeks at room temperature. Even after a storage time of one week, sufficient blowing agent is still present in the closed-cell pores of the polystyrene foams to be able to undertake adequate post-expansion of the foams with a foaming factor of 1.8 to 2.0.
Claims13
A process for producing a foamed polymer article having flame retardant properties, comprising the steps of:
- extruding a melt of styrene polymer granules, a flameproofing agent and a nucleating agent in a first extrusion step;
- injecting up to 4.3 by weight of a blowing agent comprising propane, butane or a mixture of propane and butane into said styrene polymer melt at the end of said first extrusion step, under a pressure of up to about 350 bar;
- homogenizing and cooling the styrene melt to a melt temperature of below about 150.degree. C. before a second extrusion;
- and
- subjecting the styrene polymer melt to a second extrusion to produce an extruded foamed polymer article.
Dependencies are inferred from the claim text.