The extrusion processing method of polytetrafluoroethylene film is essentially a synthesis of conventional extrusion and calendering methods, but during processing, the resin is not melted and plasticized, but raw material is processed.
The extrusion production method of PTFE film is to use the characteristic of polytetrafluoroethylene PTFE that can produce residual deformation under the action of compressive force. Adding certain additives can increase the residual deformation.
This method is to press the polytetrafluoroethylene material added with the extrusion aid into a parison with a certain density, put it into the extruder to heat it appropriately, extrude the thin strip, and finally send it to the calender roll to be calendered into a film, and then remove the auxiliary extrusion Agent can be.
The PTFE film produced by extrusion is suitable for powders with good dispersibility to be matched with appropriate extrusion aids. The extrusion aid can increase the lubrication of the PTFE molecules and reduce the pushing resistance. The commonly used squeeze aid is paraffin oil, the dosage is 17-20%. In recent years, ethylene dichloride has also been developed.
The pre-pressing rod is generally cylindrical, and it is formed by pressing in a hydraulic press. Depending on different heights, a pressure of 68.6~147Pa is used to achieve a compression ratio of 50~150.
Pushing the strip is carried out in the pushing machine. For the sake of physiology, the pressing should be carried out when the pre-compact is preheated to about 200°C, and the pressing force is 490~980Pa, and a thin strip with a diameter of 0.5~1cm can be obtained.
Before calendering, fine material strips are generally preheated in a water tank to 40~60℃ and enter the calender. The temperature of the calender roll is generally 50~80℃, and the speed of the calender roll is generally 3~10m/min. The calendering speed is generally much higher than that of pushing. Discharge speed. Therefore, in order to improve production efficiency, several pushers should be used to feed one calender.
In order to prevent the rolled film from producing wavy edges, it is necessary to press the stretched film to design a fishtail guide plate.
Depending on different needs, the extruded film needs different post-processing. If the film’s extrusion aid content is required to be very low, it must be extracted and dried at a temperature of 150~200℃ after treatment. If the film is allowed to contain a certain amount of additives, extraction is not necessary, but drying at different temperatures is required. The higher the drying temperature, the lower the content of extrusion aid. Generally the highest temperature can reach 400℃.
The cold extrusion film is actually a kind of raw film, but the performance of this film is basically equivalent to that of the cured film, with higher elongation and tensile strength, but not as good as the turned film