Effect of electrical resistivity on the adhesion and thickness of electrostatically deposited powder layers

Control of the charge decay process in an electrostatically-deposited powder layer has an important role in two areas: (1) adhesion of powder to a substrate, and (2) intensity of back corona in the deposited powder layer. If a powder is highly resistive, with resistivity greater than 10¹³ Ωm, the accumulation of charge on the deposited powder layer often causes back corona, which limits further deposition of powder. However, if the powder has low resistivity, less than 10¹⁰ Ωm, the charge decay is rapid enough that back corona does not set in and limit the deposition efficiency. However, at such low resistivity, the adhesion is so weak that the powder may not remain attached to the substrate. The role of resistivity in adhesion of powder to conducting and nonconducting substrates and the management of back corona to allow sufficient film build was studied using powders of different resistivities. Our research shows that charge-to-mass ratio (Q/M) and resistivity must both be taken into account for obtaining the desired film thickness with the necessary adhesion