Films of polypropylene

Abstract

Abstract <PICT:0840191/IV(a)/1> <PICT:0840191/IV(a)/2> Flat or tubular isotactic polypropylene film made by meltextrusion and quenching is introduced into a narrow heating zone where it is rapidly heated while travelling past an infra-red heater to a temperature between 120 DEG and 170 DEG C., and is stretched during or immediately after its passage past the heater in at least the longitudinal direction, so that a uniformly-stretched film oriented in at least one direction in the plane of the film is obtained. The film may be pre-heated, preferably to 80-110 DEG C., before being subjected to the rapid heat treatment, and a heater may also be provided in a suitable position to prevent the film from losing the heat imparted to it in the rapid heating step before stretching has been completed. After the rapid heating the film may be cooled. Preferably the film is stretched 4 to 10 times in any direction chosen. As shown, a flat film is passed from extruder 1 via quench bath 2 and nip rolls 3 to a heated roll 7, and is then stretched between roll 7 and cooled roll 8 while it is heated rapidly to 120-170 DEG C. by infra-red heater 4. The film then passes to draw rolls 5, which rotate at a higher peripheral speed than rolls 3, and is wound up on reel 6. A tubular film may be stretched substantially simultaneously both longitudinally and laterally. As shown, film passes from annular extrusion die 11 through cooling and drying means (not shown) to nip rolls 12, and is inflated by means of the tubular probe 13. The film is rapidly heated to 120-170 DEG C. by the annular infra-red heater 14 and is stretched between rolls 12 and the cooled rolls 18, which rotate at a higher peripheral speed than rolls 12. The circular heater 20 provides heated air in the stretching region and so prevents loss of heat from the film during stretching. The film is progressively flattened by rolls 15 and 16, while infra-red heaters 17 heat the film to approximately the stretching temperature, and is wound up on reel 19. Specifications 542,509, 687,532, 719,093, 741,963, 787,479, 812,387 and 822,704 are referred to.

Inventors

• 👤 George Isaac Maurice Bloom
• 👤 William Anthony Holmes-Walker
• 👤 Denis James Henry Sandiford

Bibliographic Details