| 摘要 |
A printing apparatus includes heat treatment element, a rotatable feeder roll chargeable to a predetermined first potential, a support roll chargeable to a predetermined second potential, and a matrix in the form of a flexible printing circuit. The matrix has supply apertures, each supply aperture having a first inner diameter and being surrounded by an electrically conducting control ring configured to be charged to a predetermined third potential and having a second inner diameter. The third potential is selected to control corresponding supply apertures between an open state and a closed state. The matrix has an upper surface which is covered with a protective layer having through holes, each through hole having a second diameter which is at least equal to the inner diameter of the control rings. The protective layer includes a non-magnetic metal. The matrix and the control rings are covered, at upper surfaces and bore edges, with an electrically insulating layer. The feeder roll, the support roll and the matrix are configured to transfer a dry powder from the feeder roll through the supply apertures of the matrix to an object to be printed which is conveyed over the support roll. The powder deposited on the object is fixed by the heat treatment element. |
