E.i. Dupont De Nemours and Company

David E Heyer

Albert W Forrest, Jr

Charles Nelson Jolliffe

An improved process for simultaneous biaxial stretching of a thermoplastic polymer film having beaded edges in a tenter frame consisting of gripping the beaded edges of the film with tenter clips and increasing the temperature of the beaded edges to within the film orientation temperature range prior to or during simultaneous stretching, and in subsequent stretching or heat-setting steps, by focusing heat on the beaded edges of the film. Thermoplastic films, such as polyethylene terephthalate and polyethylene naphthalate, having a final thickness of from 0.2 to 350 microns after simultaneous stretching can be prepared.

Film bead heating for simultaneous stretching

A process improvement for preparing thermoplastic polymeric film, preferably of polyethylene terephthalate, by extruding a web in melt form onto a quench drum with a surface roughness of at least 3 microinches. In casting webs of less than about 5 mils in thickness the improvement involves drawing the melt to a melt drawdown ratio of less than about 25 and spacing the die lips from the quench roll at less than about 120 mils, preferably 20 to 80 mils. It is also preferred that the flow stability index be greater than 5.

Vacuum pinning process

A process is disclosed for increasing the casting speed in manufacturing thermoplastic film and in increasing the quality of film made thereby. The film is cast, in molten form during manufacture, by means of a vacuum, onto a quench roll (casting roll) having a surface roughness of at least 3 microinches (0.08 micrometers).

Vacuum pinning of molten thermoplastic film to a roughened casting roll

A device for uniform pinning of molten web material onto a quench roll by means of at least two vacuum zones interacting through a baffle, one vacuum zone extending past the line of contact of the web on the quench roll to encompass a portion of the web edge laid onto the casting drum.

Device for uniform web pinning

A process for promoting uniform thickness in cast webs of thermoplastic material comprising use of variable air forces selectively directed toward a cast web with pinned edges along the line of initial proximity with a quenching surface. Especially useful to mitigate thinning adjacent to the pinned edges.

Pneumatic gauge adjustment of edge-pinned cast web

In the casting of molten thermoplastic web onto a moving quenching surface, the improvement which comprises passing the freshly extruded web over a bearing having a lubricating fluid on the surface thereof.

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Circleville, OH, United States of America

David E Heyer