Process for producing a shaped article by injection moulding

Claim 1

A process for the production of a shaped article of the type comprising a core of a first thermoplastics material and a covering layer of a second thermoplastics material, said process comprising: in a first step pressure-injecting said second material into a mould defining at least one impression of said article, while said second material is at an injection temperature above the softening point of said first material; then in a second step pressure-injecting into said mould said first material at an injection temperature between its softening point and said injection temperature of said second material, said first and second materials being injected in the requisite quantities for forming said covering layer and said core respectively; cooling said materials until at least the outer layer is solidified; then removing the finished article from said mould; and in which process said first material is a polythene terephthalate containing from 0 to 50% mineral fillers and said second material is a different thermoplastics material having a lower softening point than that of said polythene terephthalate; said two injection steps are performed immediately consecutively while said mould is maintained at a temperature below said softening point of said second material and below the crystallization temperature of said polythene terephthalate containing its proportion of fillers to provide a semi-crystalline core structure; and in which process in said second step said second material which was injected in said first step acts as a heat buffer slowing down temperature equilisation between said polythene terephthalate and said mould.