There are two main methods for preparing PTFE polytetrafluoroethylene microporous film. One is to add a pore-forming agent NaCl to PTFE, then make PTFE into a film, and then remove NaCl by heating and washing. The vacancies left by NaCl form pores. The minimum pore size of the microporous film made by this method is 0.1μm . The second is the mechanical stretching method. The microporous film made by the modified method has a special microfiber connection island-like "knot" structure, which is currently the main method for preparing PTFE microporous film.
In the 1960s, PuPont first used a uniaxial stretching method to prepare PTFE stretched membranes, but the size of the micropores, porosity and membrane strength were not ideal. In the mid-70s, American Gore Company successfully developed expanded PTFE microporous film using biaxial stretching technology. After that, Japan made great progress in research in this area and applied for a number of patents. my country began to develop PTFE stretch membranes after the 1970s, but for a long time it has remained in the uniaxial stretching process. Since the 1990s, some units have developed and produced biaxially stretched microfiltration membranes.
The PTFE polytetrafluoroethylene fine powder and additives are fully mixed and then enter the extruder. The powder is pushed to extrude a strip of PTFE, and then it is rolled into a diaphragm under the rolling machine. After heating to remove the additives, it can be stretched in the vertical and horizontal directions, and the biaxially stretched microfiltration membrane is obtained by heat treatment, shaping, cutting and winding.