Device for blowing and stretching plastic packaging film and method thereof

A plastic film blowing and stretching device, comprising:

• at least one first blow-expanding mechanism, which comprises at least one extrusion machine, at least one mold head, and at least one air ring, wherein the extrusion machine of the first blow-expanding mechanism is operable to subject a primitive plastic film made of a material of one of polyvinyl chloride (PVC), polylactic acid (PLA), and polyethylene terephthalate (PET) to initial extrusion at a temperature of 140° C.-180° C., the air ring being arranged above the mold head, the mold head being arranged above the extrusion machine, for subjecting the primitive plastic film to primary blow-expanding so as to achieve a volume in which the primitive plastic film has a lateral opening ratio of 1:1;
• at least one pair of front-stage press rollers and middle-stage press rollers, which are sequentially operable to subject the primitive plastic film that has been subjected to primary blow-expanding by the first blow-expanding mechanism to primary longitudinal press-flattening and pull-stretching;
• at least one second blow-expansion mechanism, which comprises at least one heating-extension oven, at least one annular water tank, and at least one movable air charging device, wherein the heating-extension oven is arranged at a location at an upper side of the second blow-expansion mechanism and below the middle-stage press rollers, so that the heating-extension oven subjects the primitive plastic film that has been subjected to the primary press-flattening and pull-stretching to heating to a temperature of 160° C.-220° C., the annular water tank being arranged above the heating-extension oven and filled, in an interior thereof, with water having a temperature of 10° C.-20° C. for shaping the primitive plastic film that has been heated by the heating-extension oven, the movable air charging device being arranged above the annular water tank and comprising at least one movable air charging nozzle and an air charger, the movable air charging nozzle being connected to the air charger, the movable air charging nozzle being extendable into an interior of the primitive plastic film that has been shaped by the annular water tank in order to supply a pressure of 1.1-1.6 atm into the interior of the primitive plastic film to subject the primitive plastic film that has been subjected to primary longitudinal press-flattening and pull-stretching and has been heated and shaped by the heat-extension oven and the annular water tank to heating and blow-expanding to achieve a volume in which the primitive plastic film has a lateral opening ratio of at least 2:1 so as to form a shaped plastic film;
• and
• at least one pair of rear-stage press rollers, wherein a rotational speed difference of thee rear-stage press rollers and the front-stage and middle-stage press rollers is between 30%-80%, and the rear-stage press roller are operable to subject the shaped plastic film that has been subjected to blow-expanding by the second blow-expansion mechanism to secondary longitudinal press-flattening and pull-stretching so as to supply a plastic packaging film product having uniform blow-expansion and pull-stretching stress and quality in both lateral direction and longitudinal direction.