| 摘要 |
Shaped expanded thermoplastic articles are made by heating under pressure between platens a mix comprising a thermoplastic material and a blowing agent, cooling the mix, releasing the pressure, cutting the intermediate product to the desired shape and heating to effect expansion. Specified thermoplastic materials are polymers and copolymers of vinyl chloride, styrene, butadiene, acrylonitrile, acrylates and methacrylates, natural and synthetic rubber, and polyamides. The blowing agents include bicarbonates, azo compounds, sulphonyl hydrazides, hydrazones, organic nitrates, nitroso compounds, substituted ureas and salts of urea or substituted urea. The mix also preferably contains a hydrocarbon or halogenated hydrocarbon solvent of boiling point above 80 DEG C. (e.g. tetrachlorethane), and may also contain a plasticizer (e.g. dioctyl phthalate), and lead stearate. The intermediate product is preferably in the form of a flat sheet which may be cut by a saw or cylindrical cutter. The initial heating is preferably not in excess of 130 DEG C. and the cooling is down to 20 DEG -30 DEG C. Mention is made of the use of the products as fishing floats and marker buoys. Specifications 818,224 and 876,870 are referred to.ALSO:Shaped expanded thermoplastic articles are made by heating under pressure between platens a mix comprising a thermoplastic material and a blowing agent, cooling the mix, releasing the pressure, cutting the intermediate product to the desired shape, and heating to effect expansion. The intermediate product is preferably in the form of a flat sheet and may be cut by a saw or by an axially rotated cylindrical cutter. The initial heating is preferably not in excess of 130 DEG C. and the cooling is down to 20 DEG -30 DEG C. Specified thermoplastic materials are natural and synthetic rubber, polymers and copolymers of vinyl chloride, styrene, butadiene, acrylonitrile, acrylates and methacrylates, and polyamides. The blowing agent may be a bicarbonate, azo compound, sulphonyl hydrazide, hydrazone, organic nitrite, nitroso compound, substituted urea, or a salt of urea or substituted urea. The mix also preferably contains a hydrocarbon or halogenated hydrocarbon (e.g. tetrachlorethane), and may also contain a plasticiser (e.g. dioctyl phthalate), and lead stearate. Mention is made of the use of the products as fishing floats and marker buoys. Specifications 818,224 and 876,870 are referred to. |
