Unsaturated polyester, epoxy resins come out after 40. MICA paper appeared to free people from the MICA scarcity dilemma.
Since the 50 's, has been widely used as base materials for synthetic resin, unsaturated polyester and epoxy impregnated with plastic insulation for high-voltage motor coil. Polyester series motor liner used in insulation, enamel and varnish, developed the e-class and b-class low-voltage electrical insulation, so that the further decline in the size and weight of the motor. Sulfur hexafluoride used high voltage apparatus, and give it to the capacity development of miniaturization. Circuit breakers of air insulated and transformer oils and paper insulation partially replaced by sulfur hexafluoride.
60 containing heterocyclic and aromatic resin has been developed, such as polyimide and poly aromatic amides, aryl sulfone, pps, such as h-class and high heat-resistant grade of material. The synthesis of heat-resistant material for the later development of class f, class h Motors has created favorable conditions. Polypropylene films in this period is also successfully used in electrical capacitors.