Extrusion method and apparatus

Method of producing polyethylene terephthalate film which comprises:

• a. extruding molten polyethylene terephthalate in the form of a generally continuous film from a slot orifice at a substantially predetermined rate,
• b. feeding said molten extruded film onto the peripheral surface of a quenching drum in a direction which intersects substantially tangentially with the periphery of said drum, said drum surface being cooled to a conventional quenching temperature below the solidification temperature of said polymeric material, and said drum being rotatably driven to advance the film thereon at a linear rate greater than said rate of extrusion whereby said film is stretched, and
• c. in the gap between said slot orifice and said drum surface, mechanically deflecting said film while still in molten condition from a rectilinear path between said orifice and drum surface by passing the film while in such gap over its full width partially around a rotatable control roller having a smooth polished surface disposed on the opposite side of said film from said drum and rotated at a linear rate substantially equal to said drum, said roller having a radius less than one-fourth that of said drum and being maintained at a temperature of at least about ambient room temperature but less than said drum temperature at the initial point of contact of said film with said quenching drum to thereby provide a skin at the directly proximate stratum of film contacting said control roller surface, whereby lateral contraction of the film is substantially arrested on said roller, said film being in contact with said control roller over an angle of up to about 180.degree. and sufficient to provide slip-resisting frictional contact between said film and said control roller surface, the clearance space between said extrusion slot orifice and the initial point of contact of said film with said control roller surface being not more than about 20 mm.

In an apparatus for forming polyethylene terephthalate films by extrusion along an extrusion plane in a generally downward direction of a molten polyethylene terephthalate through a downwardly opening slot orifice onto the surface of a rotatable quenching drum maintained at a conventional quenching temperature below the solidification temperature of the polymer, said drum being located beneath said orifice with the peripheral surface region thereof initially contacted by said film extending obliquely in one direction through and beyond the extrusion plane, the improvement comprising a continuous smooth polished control surface of a width at least equal to the width of said film and maintained at a temperature of at least about room temperature but less than the temperature of the quenching drum surface at the initial point of contact of said film with said developing drum surface to thereby provide a skin at the directly proximate stratum of film contacting said control surface, said control surface being movable through a continuous path including an arcuate portion with a radius less than one-fourth that of the quenching drum, at least said arcuate path portion being disposed in the gap between said orifice and said quenching surface for contact with the entire surface of the surface of said film opposite said quenching drum and projecting through and beyond said extrusion plane in the opposite direction to said drum to produce a bow-shaped deflection in the film path in said gap of an arcuate extent up to about 180.degree. and sufficient to provide slip-resisting friction contact between the film and said control surface, and means for rotating the quenching drum surface and for advancing said control surface in the same direction as the film in contact therewith and at substantially the same linear speed which is higher than the linear rate of extrusion of said film in order to stretch said film, the clearance space between said extrusion slot and the initial point of contact of said film with said control surface being not more than about 20 mm.