Monoaxial orientation of tubular PET parisons - by tensile drawdown through coaxial clamps near the glass transition temp.

摘要

Tubular profile of a crystallisable thermoplastic is converted into an oriented tubular parison by heating the profile sufficiently to obtain ductility, compressing part of the profile radially and then drawing more of the profile through one or more radially restricted orifices to reduce the profile wall thickness and induce a degree of orientation which would match that obtained by monoaxial extension of a flat plaque of the same material at the same temperature to the same degree of thickness reduction. Equipment for such a process is described having twin radially contracting clamps which can then be separated coaxillay relative to the profile, the clamps being mounted on crossheads driven by contrarotating lead screws. Esp. suitable for preparing parisons of polyethylene terephthalate for producing blow-moulded containers, esp. where excessive initial extension is reqd. to permit partial contraction of the parison during dilation to obtain a balance of biaxial orientation when making small containers (less than 0.5L).