Method for the manufacture of thin-walled shaped articles of crystalline thermoplastic material

A method for manufacturing thin-walled articles from crystalline thermoplastic material by thermoforming the articles in a web or sheet of said thermoplastic material and removing the shaped articles from said web or sheet, said thermoplastic material having a critical crystalline melting temperature range with a lower limit temperature T.sub.C and an upper limit temperature T.sub.M and said method further including temperature conditioning of said web or sheet for thermoforming, characterized in that said temperature conditioning involves at least two steps;

• namely:
• (a) developing by heating and/or cooling a preliminary temperature profile across the thickness of said web or sheet in which the core material of the web or sheet is at a temperature close to but lower than the critical crystalline melting temperature range of the said crystalline thermoplastic material and wherein said core is elastically deformable and the outer surface regions of the web or sheet are at lower temperatures than the core material and not thermally formable;
• and
• (b) developing a final temperature profile for the thermoforming step by reheating one or both of said outer surface regions of said web or sheet to a temperature within said critical crystalline melting range whereby the said crystalline thermoplastic material of the outer surface regions becomes elastically deformable, whereas the said core material is retained in an elastically deformable state at a temperature adjacent to but lower than said critical crystalline melting temperature range.