| 摘要 |
The invention relates to a method of producing a multi-layer, preferably two-layer, sandwich of a foamed polystyrene film with a co-extruded unfoamed film, in particular for further working into labels or shaped bodies utilizing the shrinkability of the films, in which a polystyrene resin composition, together with nitrogen as expansion agent and a pore-former, is extruded out of the nozzle of an extruder and the extruded composition is expanded prior to cooling to below the softening point. In order to obtain a production of foamed polystyrene films which is economical as to material and is as unsusceptible to breakdown as possible and also as insensitive to aging as possible and readily printable, the invention proposes that, as expansion agent, there be used exclusively per kilogram of foamed film 1/30 to 1/50 nitrogen (measured in standard liters) of the weight per unit area of the film (measured in grams per square meter), in combination with a powdered mixture of sodium bicarbonate and citric acid, and that the stiffness/surface-nature of the film be controlled by the expansion ratio.
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