Method for coating a surface with a transferable layer of thermoplastic particles and related apparatus

A method of coating a donor surface with a layer of thermoplastic particles, the method comprising:

• a) providing a supply of the thermoplastic particles suspended in a fluid, the fluid being a liquid that does not wet the donor surface or being a gas, the surface energies of the thermoplastic particles and of the donor surface being selected such that the particles have a higher tendency to adhere to the donor surface than to one another;
• b) applying the fluid to the donor surface, by an applying system, in a manner to cause the particles suspended in the fluid to adhere to the donor surface so as to form a substantially continuous particle coating on the donor surface as the donor surface is moved relative to the applying system;
• c) causing fluid flow within an interior plenum of a housing and over a portion of the donor surface partially disposed within the plenum, the fluid flow being of sufficient magnitude to entrain particles that are not in direct contact with the donor surface and insufficient to entrain particles that are in direct contact with the donor surface;
• and,
• d) extracting fluid and particles which are not in not direct contact with the donor surface from the plenum, so as to leave adhering to the donor surface a particle coating that is substantially only a single particle deep;
• the plenum having a rim adjacent to the donor surface, the rim being configured to prevent egress of particles and/or fluid from a sealing gap defined between the rim of the housing and the donor surface.