Tubular Thermoplastic Film (Patent No: 726090)

Inventor: Hansen, Kenneth T.

Location: Sherwood Park

Comments: N/A

Description:

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of thin-walled thermoplastic layflat tubular film of predetermined width which comprises extruding a melt of thermoplastic material through an annular die to form a seamless tubing, continuously withdrawing and flattening said tubing at a predetermined distance from the point of extrusion and maintaining a substantially constant continuous bubble of a gaseous medium in the section of the tubing extending between the point of extrusion and the point of flattening, the quantity of said gaseous medium constituting said bubble being such as to inflate the tubing while in the formative plastic state, characterised in that the predetermined width of the layflat tubing is obtained by passing the inflated tubing in the unset condition through an annular sizing means located on or beyond the frost-line from the point of extrusion and contacting said tubing so as to simultaneously chill it to the set condition and control its diameter to such an extent that said predetermined width is obtained when the tubing is converted to a layflat form.

2. A process for the production of thin-walled thermoplastic layflat tubular film of predetermined width which comprises extruding a melt of thermoplastic material through an annular die to form a seamless tubing, continuously withdrawing and flattening said tubing at a predetermined distance from the point of extrusion and maintaining a substantially constant continuous bubble of a gaseous medium in the section of the tubing extending between the point of extrusion and. the point of flattening, the quantity of said gaseous medium constituting said bubble being such as to inflate the tubing while in the formative plastic state, characterised in that the predetermined width of the layflat tubing is obtained by passing the inflated tubing in a cooled but unset condition through an annular sizing means located on or beyond the frost-line from the point of extrusion and contacting said tubing so as to simultaneously chill it to the set condition and control its diameter to such an extent that said predetermined width is obtained when the tubing is converted to a layflat form.


3. A process as claimed in Claim I or 2 wherein the bubble of gaseous medium is isolated between the point of extrusion and the point of flattening of the tubing.


4. A process as claimed in Claim 1 or 2 wherein the sizing collar is circumferentially adjustable in contact with the outer surface of the inflated tubing.


5. A process as claimed in Claim 2 wherein the tubing is precooled by an external air flow directed on and around said tubing through an air cooling ring located in the vicinity of the point of extrusion of the tubing.


6. A process as claimed in Claim 2 or 5 wherein the amount of air directed on and around said tubing through said air ring is adjusted so as to position the frost-line of the tubing on or slightly beyond the sizing means from the point of flattening of said tubing.

7. A process as claimed in Claim 1 or 2 wherein the gaseous bubble in the tubing is expanded until the latter touches the sizing means uniformly at or slightly beyond the frost-line from the point of extrusion of said tubing.


8. A process as claimed in Claim 1 or 2 wherein the sizing means consists of at least one turn of tubing in the form of a helix or a jacketed cylinder through which is circulated a cooling medium.