Apparatus for stretching thermoplastic

Claim 1

APPARATUS FOR STRETCHING ORGANIC THERMOPLASTIC FILMS HAIVNG CONTINUOUSLY BEADED LONGITUDINAL EDGES, COMPRISING. (A) ROTATING FILM FEED ROLLS MOUNTED AT ONE END OF SAID APPARATUS, (B) FILM PULLING ROLLERS MOUNTED AT THE OTHER END OF SAID APPARATUS, ROTATING AT A PERIPHERAL SPEED AT LEAST AS GREAT AS THAT OF SAID FEED ROLLS, (C) ELONGATE FILM-EDGE GUIDE FRAMES MOUNTED BETWEEN SAID FEED ROLLS AND SAID PULLING ROLLS AND COPLANAR WITH THE FILM PASING BETWEEN SAID ROLLS SAID GUIDE FRAMES DIVERGING LATERALLY FROM THE CENTERLINE OF SAID STRIP IN THE DIRECTION FROM THE FEED ROLLS TO THE PULLING ROLLS, (D) EACH OF SAID GUIDE FRAMES INCLUDING VERTICALLY SPACED, LONGITUDINALLY CONTINUOUS WALL ELEMENTS DEFINING BETWEEN THEIR PROXIMATE EDGES A CONTINUOUS SLOT SIZED TO RECEIVE AN EDGE OF SAID FILM WITH ITS BEAD CONSTRAINED BY SAID WALL ELEMENTS TO TRAVEL OUTWARDLY OF SAID CENTERLINE BY SLIDING ENGAGEMENT OF THE BEAD WITH THE OUTER SURFACES OF SAID WALL ELEMENTS; (E) AT LEAST THE SURFACES OF SAID WALL ELEMENTS WHICH ENGAGE SAID BEAD BEING FORMED OF CONTINUOUS STRIPS OF SOLID MATERIAL HAVING A LOW COEFFICIENT OF SLIDING FRICTION WITH RESPECT TO THE MATERIAL FORMING SAID THERMOPLASTIC FILM.