Articles cellulaires mousses en polymère thermoplastique

摘要

Cellular thermoplastic polymers are made flame-resistant by incorporating in them an organic halogen-containing flame-proofing agent and, as a synergist, an indigo compound. The polymer is either (a) an alkenyl aromatic polymer (e.g. styrene, alpha-methyl styrene or a nuclear halogenated or alkylated derivative thereof) or a copolymer thereof with up to 50% of another monomer (e.g. acrylonitrile) or (b) a copolymer of 1-97% by weight of methyl methacrylate and 99-3% by weight of an alkenyl aromatic monomer. The flame-proofing agent is preferably a brominated aliphatic, cycloaliphatic or alkylaromatic hydrocarbon or aliphatic ether or ester (e.g. propionate or phosphate) containing at least 45% by weight of bromine. The indigo compound is preferably indigo white or an indigo derivative of formula: where R is an -NH- group or -S-; X and Y are hydrogen, halogen or lower alkyl; and Z is hydrogen, halogen or a radical of formula-SO3M where M is hydrogen or an alkali metal. The foamable composition may also include a hydrobromic acid acceptor (e.g. sodium acetate, magnesium oxide, magnesium hydroxide, zinc oxide, calcium oxide, calcium carbonate or sodium bicarbonate) or a surfaceactive agent (e.g. a sodium alkyl sulphonate, sodium lauryl sulphate or an alkyl phenyl polyethylene glycol ether) which latter may be added together with the indigo compound. The foam may be made by (1) feeding the granular polymer to a first section of an extruder where it is heated to about its melting temperature and forwarded through a sealing plate or disc into (2) a second section where it is mixed with a volatile liquid (e.g. an aliphatic hydrocarbon, ether or alhogenated hydrocarbon) and fed into (3) a mixing section where it is agitated and cooled and forwarded to a (4) a mixer cooler where the ingredients are thoroughly blended, brought to a uniform temperature between 60 DEG and 130 DEG C., under pressure, and (5) extruded into a zone of lower pressure (e.g. the atmosphere) to cause expansion of the extruded material. As an alternative to step (4), the extruded product may be quickly cooled and then crushed or ground to form latent foaming granules. The flame-proofing agent and the indigo compound may be added at any point prior to extrusion. Examples describe the production of polystyrene foams.