Thermoforming and heat shrinking for forming containers

A method for producing a thermoplastic, unitary, open-ended container-shaped article having a depth to diameter ratio of less than 1.0 and having biaxially oriented sidewalls and a bottom comprised of a central unoriented portion surrounded by a biaxially oriented transparent portion, said method comprising:

• securing a sheet of thermoplastic at its orientation temperature in a forming tube;
• providing a plunger and a plunger follower, the plunger and plunger follower being axially aligned and the plunger including a circumscribing sharp edged lip about a select area of a leading surface of the plunger for gripping the thermoplastic sheet;
• plug forming said thermoplastic in a first stage with the plunger and the plunger follower, wherein a portion of said thermoplastic sheet is gripped by the lip between the plunger and plunger follower so that the portion of the thermoplastic sheet circumscribed by the lip is prevented from becoming oriented;
• blow forming said plug formed thermoplastic to yield said container-shaped intermediate;
• and
• heat shrinking said intermediate to a depth to diameter ratio of less than 1.0 onto a male form having a predetermined size, shape and texture.

An apparatus for producing a short drawn, thermoplastic, container-shaped intermediate from a sheet of thermoplastic, said intermediate comprised of biaxially oriented sidewalls and a bottom having a central unoriented portion surrounded by a biaxially oriented portion, said apparatus comprising:

• means for securing said sheet of thermoplastic in a forming tube;
• an axially aligned plunger and plunger follower, the plunger including a leading surface facing the plunger follower, the leading surface including a circumscribing sharp edged lip for gripping the sheet of thermoplastic about a select portion of the leading surface to prevent orientation of a portion of the thermoplastic sheet corresponding to the select portion of the leading surface which is circumscribed by the lip;
• means for bringing the leading face of the plunger and the plunger follower together to sandwich the portion of the thermoplastic sheet while the plunger forces the sheet into a container shape;
• and
• means for introducing air pressure into the interior of the container-shaped intermediate to further orient the thermoplastic sheet.