Diamond dotted polyester film is also known as DPF. The use of this B-stage resin coated film increases the mechanical strength of transformer coils. It is produced by coating modified epoxy resin in diamond dot patterns on electrical insulating film. The size of the dots are carefully designed and arranged to cover only 36% of the surface, remaining 64% free for optimum SF6 gas distribution.
After curing, the prepreg resin cures from stage B to stage C, adhering to any metallic surface and creating micro channels for optimal gas distribution. The bonding strength is adequate to support effective gluing in unsupported coil design.