Reasons that affect the capacity of film capacitors:

The capacity of the film capacitor depends on the area of ​​the film metal layer, so the decrease in capacity is mainly caused by the reduction of the area of ​​the metal plating layer affected by external factors. In the capacitor manufacturing process, there is a trace of air between the film layers, and it is difficult to completely eliminate it. When the capacitor is working, the air may be ionized under the action of the electric field. Ozone is produced after air ionization. Ozone is an unstable gas that decomposes into oxygen at room temperature. It is a strong oxidant and can instantly complete oxidation at low concentrations. The metal coating of the metallized film (the composition is Zn/Al) is oxidized immediately after encountering the oxygen decomposed by ozone, forming transparent and non-conductive metal oxides ZnO and Al2O3. The actual performance is that the plate area is reduced and the capacitor capacity is reduced. Therefore, eliminating or reducing the air between the membrane layers can slow down the capacitance decay. When the air between the film layers is invaded by external moisture, the breakdown potential of the air will decrease, accelerate the ionization of the air, produce a large amount of ozone, oxidize the metal coating of the metalized film, and the capacity of the capacitor will drop rapidly.