Various processing technologies have been developed to produce unidirectional and bidirectional stretched PET films. Typical processing includes the following steps:
① PET extrusion with hanger die head;
② quenching stage;
③ deformation stage;
④ Post-processing stage.
At the beginning of processing, the extruded molten sheet is immersed in a water bath to quench. However, the surface of the film product produced in this way will cause defects due to local boiling water, so the mixture of 80% glycerin and 20% water instead of water improves the quality of the film. After quenching with quench roller (surface temperature 15~18℃). In processing, a positioned inert gas flow is added to the upper surface on each side of the molten film, where the film first makes contact with the quench roll surface.
After quenching, the film, regardless of crystallinity, is heated above T, with a blower heater, or a quartz electric heater is used in the subsequent forming process. At this stage, the temperature of the thermal operating window is 80 to 120 ° C, and the temperature is usually maintained at 80 to 100 ° C. After the sheet is softened, one-way stretching, sequential bidirectional stretching or simultaneous bidirectional stretching is carried out, and the stretching method is selected according to different applications.
Design for simple unidirectional stretching of PET film with a variety of different rollers. The roller assembly of the unidirectional drawing system comprises a low speed roller, an idling roller and a fast roller. The production process of PET heat shrink film. This film is widely used in the packaging of articles of various shapes, sealing or sealing articles with thermal shrinkage, and can place the packaging in a state of heating. In the process of heat shrink sheet processing, at 80 to 135 ° C, the film is stretched to 2 times, and the film is cooled to room temperature under tension conditions. Above 80℃, the films produced by this method shrink 35% in TD direction and 15% in MD direction. At 180~200 ° C, the production of tape film is stretched in one direction from about 1.5 times to 2 times, and the heat curing temperature under the action of tension is 190~200 ° C, so that there is no shrinkage.
One of the first patents for sequential stretching. The softened substrate is first stretched in the width direction and then in the length direction, or the stretching step is reversed. The temperature of the second stage should be at least the same as the temperature of the first stage, or 5 to 30 ° C higher than the first stage, but not more than 120 ° C, at which temperature the heat activated crystals increase. When processing PET films for photographic purposes, they are first stretched in the width direction and then in the length direction. After thermal curing at about 190~200 ° C, the film is covered by a layer of colloidal liquid, which is vinylidene chloride.
Regarding the continuous synchronous biaxial stretch PET film, the device for synchronous biaxial stretch is a frame, the edge of the extrusion film is thicker than the rest of the place, so the frame can safely grip the film. The invention relates to a preparation process of a letter-oriented PET film with a glazed surface. In the process, the amorphous film is initially stretched at 112 ° C to 4x4, producing a bright surface. The same results can be obtained by stretching the film to 2x2, then cooling the stretched film to room temperature, heating and stretching again to obtain a luster.
