| 摘要 |
<p>In a method of injection moulding plastics articles having a solid skin but a porous core, by injecting the core inside the skin matl. into the mould: the core matl. contains a bubble-former which produces in it, under the thermodynamic conditions in the mould, macroscopic bubbles (i.e. up to several cm diameter); the injection nozzle for the core matl. contg. this bubble-former extends into the discharge opening into the mould, thereby maintaining thermodynamic conditions which prevent bubble formation until the matl. actually enters the mould. Pref., micropore-producing, chemical expanding agent is also introduced into the core matl., opt. also into the skin matl. The substance for producing the large bubbles is pref. a gas, and in particular a granular transporting agent contg. it, e.g. wood chips soaked in water (30-60% by vol. of chips in relation to the core matl., contg. 20% humidity) are used. Alternatively, water and/or steam is injected into the core matl. Further bubble-producing agent may be injected by a needle into the mould as the core matl. enters. The core and skin matl. may be of the same plastics. Process gives a considerable reduction in the density.</p> |
