Molding of elongate, hollow, biaxially oriented thermoplastic shaped articles

Claim 1

A process for the manufacture of an elongate, rigid, tubular, biaxially oriented thermoplastic, hollow thin-walled shaped article which is open at both ends, has an internal diameter or inscribed diameter equal to at least 2 cm, and a length to diameter ratio of at least about 10/1 comprising (i) introducing into an elongate mold cavity, the internal configuration and dimensions thereof corresponding to the exterior surface area of the desired shaped article, and aligning along the longitudinal axis thereof, a long tubular thermoplastic blank which is open at both ends and which is heated to the biaxial orientation temperature of said thermoplastic; (ii) expanding under internal fluid pressure in the absence of mechanical stretching means said heated tubular blank to simultaneously, both longitudinally and transversely, uniformly stretch same, at least to the natural biaxial drawing ratio thereof, but to a value in the transverse direction of less than 100% of that ultimately desired so as to avoid any contact between the tubular blank and the internal walls of the mold cavity prior to the completion of said longitudinal stretching; (iii) next further expanding said heated tubular blank, under increased internal pressure, completely against the internal walls of the mold cavity to thus completely shape said ultimately desired shaped article; and (iv) thence cooling said desired shaped article and releasing all pressure therefrom.