The present invention provides a method of forming an article, for use as a beverage cup, or as a container from a molten plastic composition comprising a polymer and a blowing agent. The method provides a mould 2 having first part 12 with a first surface 22a and second part 14 with a second surface 24a, closing the mould thereby defining a cavity between first and second surfaces, injecting molten plastic composition 50 into the cavity, the composition including a polymer and a physical blowing agent, applying a packing pressure, the composition in contact with the surfaces being cooled to form first and second solid skins 4, 6, during the injecting step (c) and the packing step (d), the injection pressure and the packing pressure, respectively, are maintained above a minimum pressure threshold in at least one second region 32 of the cavity to maintain the physical blowing agent as a gas dissolved in the polymer so that substantially no gas bubbles are formed in the at least one second region, during a mould opening step (e), at least some of the molten plastic composition is exposed to an external pressure lower than a minimum pressure threshold to form in the article at least one first portion comprising expanded cellular foam formed from the plastic composition, and prior to the opening step (e), the plastic composition in the at least one second region of the cavity has been cooled so as to be fully solidified to form in the article at least one second portion comprising a substantially homogeneous, solid phase, unexpanded plastic composition
展开▼
