Separating discharge in transfer of insulating sheet

Separating discharges are measured with a model of sheet transfer system, where a negatively or positively electrified PET (polyethylene terephthalate) sheet is separated from a grounded metal cylinder. The discharge bridges the wedge-shaped air gap and spreads on the sheet. Photographs of discharge light are taken with an image-intensifier-aided video camera, and powder figures are made by sprinkling toners on the sheet. A polarity effect is shown in the discharge figures: a tree-like discharge occurs on the negatively electrified sheet and an oval-shaped discharge appears on the positively electrified sheet. For negative electrification at a surface charge density of about -0.4×10^-4 C/m², there occurs a tree-like discharge which has many branches that may be as long as 70 mm, and the charge transfer of one discharge pulse can be as high as 3000 pC. The discharge figures on the negatively electrified sheet indicate that a positive surface discharge tends to stretch until its tip meets the neutralized zone produced by preceding discharges