Layflat Tubular Film Width Control (Patent No: 726076)

Inventor: Canadian Industries Limited

Location: Montreal, PQ

Comments: N/A

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

1. A method of producing 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 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 said layflat tubular film is continuously controlled and any substantial deviation therefrom is obviated by passing said tubing after flattening thereof over a detecting means consisting essentially of a metered gas tube extending transversely and beyond each side of said, tubing and provided on its surface contacting said tubing with gas escaping means located on each side thereof and extending at least partially under said tubing on each side thereof so that any change in the width of said tubing results in an increase or a decrease of the gas escaping means area and hence in a variation of the gas pressure inside the metered gas tube, and controlling by means of said gas pressure variation compensating readjustment of the shape of the tubular film bubble.

2. A method of producing thermoplastic layflat tubular film of predetermined width as claimed, in Claim l wherein the seamless tubing, while in the formative plastic state, is cooled by directing and applying a controlled volume of an external stream of a cooling gaseous medium impinging circumferentially on said tubing.

3. A method of producing thermoplastic layflat tubular film of predetermined width as claimed in Claim 1 wherein the gaseous medium which is introduced into the seamless tubing so as to inflate the latter also acts as the cooling medium to convert said seamless tubing from its formative plastic state to the set condition.

4. A method of producing thermoplastic layflat tubular film of predetermined width 'as claimed in Claim 1 or 2 wherein the shape of the tubular film bubble is readjusted by varying the rate of cooling gaseous medium impinging circumferentially on the seamless tubing.

5. A method of producing thermoplastic layflat tubular film of predetermined width as' claimed in Claim 1 or 3 wherein the shape of the tubular film bubble is readjusted by varying the volume of gaseous medium which is introduced into the seamless tubing so as to inflate it.

6. A method of producing thermoplastic layflat tubular film of predetermined width as claimed in Claim l, 2 or 3 wherein the controlling, means is located in the layflat tubing path close to the flattening point of the inflated tubing.

7. An apparatus for the production of thermoplastic layflat tubular film of predetermined width comprising an annular film extrusion die film flattening, means located at a point away from said die, a source of gaseous medium for inflating said film between said die and flattening means, a film width detecting means in the path of said film beyond said flattening means and consisting essentially of a metered gas tube extending transversely and beyond each side of said film sliding thereon and provided on its surface contacting said film with gas escaping means located on each side thereof and extending at least partially under said film on each side thereof so that any change in the width of said film results in an increase or a decrease of the gas escaping means area and hence in a variation of the gas pressure inside the metered gas tube, and controlling means coupled to said metered gas tube and adapted through said gas pressure variation to effect the necessary readjustment of the inflated tubular film.

8. An apparatus as claimed in Claim 7 wherein the gas escaping means are holes or slits.


9. An apparatus as claimed in Claim 7 or 8 wherein the metered gas tube is extendable.