Charge decay enhancement in polymer powders using plasma treatment

Slow charge decay characteristics of polymer powders results in occurrence of back corona which adversely affects the integrity of the powder film. The surface property that primarily governs the charge decay characteristics and back corona is the surface resistivity of the powder layer. Since the charge decay through these highly resistive polymers is primarily a surface phenomenon, surface modification was used to modify charge decay characteristics of acrylic and epoxy polymer powders. A fluidized bed type plasma reactor was built for surface modification of polymer powders. A 12 kV power supply at 700 Hz was used to generate plasma between copper electrodes in the reactor using argon as feed gas. The charge decay characteristics of untreated and plasma treated acrylic polymer powder samples were measured at different relative humidities varying form 20% to 70%. The charge decay time constant for plasma treated powder was 458 minutes at 18%RH whereas for untreated powder it was 996 minutes. These values became 11 minutes for plasma treated powder and 20 minutes for untreated powder at 65% RH. To study the effect of plasma treatment time on charge decay enhancement, an epoxy powder was plasma treated for 1,2,4 and 10 minutes and charge decay time constants measured. Treatment times of 1,2 and 4 minutes increased the charge decay properties, but there was no further improvement over 4 minute exposure time.