Quenching molten thermoplastic film

Claim 2

In an apparatus for quenching molten thermoplastic film comprising a movable quenching surface, an extrusion die positioned above the quenching surface to extrude a polymeric film onto the quenching surface and lateral point pinning means positioned above the quenching surface and over each lateral edge of the film, the improvement which comprises means for directing additional pinning force onto the surface of the film at least over the areas of the extruded film inward from each lateral pinned edge and having the highest temperature, to prevent localized thinning of the film.

Claim 3

An apparatus of claim 1 wherein the lateral point pinning means are electrostatic point probes.

Claim 4

An apparatus of claim 1 wherein the means for directing additional pinning force are vernier air jets.

Claim 5

An apparatus of claim 1 further comprising a pressure box for applying a uniform field of air pressure onto the surface of the film after its touchdown onto the quenching surface.

Claim 6

In an apparatus for quenching molten thermoplastic film comprising a movable quenching surface, an extrusion die positioned above the quenching surface, a bearing positioned between the extrusion die and the normal touchdown point of a polymeric film extruded from the die onto the quenching surface and means for providing a layer of fluid on the surface of the bearing; an electrostatic probe positioned over each lateral edge of the film to impart an electrostatic charge thereto; and a pressure box for applying a uniform field of air pressure onto the surface of the thermoplastic film after its touchdown onto the quenching surface; the improvement which comprises a multiplicity of point pinning means positioned within the uniform air pressure field generated by the pressure box and at least over an area adjacent each lateral edge extending about from the point of electrostatic edge pinning in a diagonal direction over that mobile area of the extruded film having the highest temperature.

Claim 7

In an apparatus for quenching molten thermoplastic film comprising a movable quenching surface, an extrusion die positioned above the quenching surface, a bearing positioned between the extrusion die and the normal touchdown point of a polymeric film extruded from the die onto the quenching surface and means for providing a layer of fluid on the surface of the bearing; an electrostatic probe positioned over each lateral edge of the film to impart an electrostatic charge thereto; and a pressure box for applying a uniform field of air pressure onto the surface of the thermoplastic film after its touchdown onto the quenching surface; the improvement which comprises a multiplicity of point pinning means positioned within the uniform air pressure field generated by the pressure box and at least over an area adjacent each lateral edge extending about from the point of electrostatic edge pinning in a diagonal direction over that mobile area of the extruded film having the highest temperature.

Claim 8

The apparatus of claim 1 wherein the means for directing additional pinning force are vernier air jets positioned along the lateral edges of the film in an area extending inwardly on a diagonal path from the edge of the film.