Apparatus for coating a surface with a transferable layer of thermoplastic particles, and related methods

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,
• b) 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;
• c) applying the fluid to the donor surface, by a particle applicator, 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 surface as the surface is moved relative to the particle applicator, and
• d) causing fluid flow over the donor surface, 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 therewith, thus extracting fluid and surplus particles that are not in direct contact with the donor surface, so as to leave adhering to the surface a coating that is substantially only a single particle deep.

A coating station serving to coat an endless donor surface or portions thereof during each passage of the donor surface past the coating station with a layer of thermoplastic particles to form a particle coating that is substantially only a single particle deep, at least selected regions of the particle coating being transferable from the donor surface to a substrate, the coating station comprising:

• a) a supply system operative to supply 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 particles have a higher tendency to adhere to the donor surface than to one another,
• b) an application device for applying the fluid to the donor surface 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,
• c) a cooler disposed to operatively cool the donor surface prior to the applying of the fluid to the donor surface, and
• d) a surplus extraction system operative to cause a fluid flow over the donor surface, the fluid flow being of sufficient magnitude to entrain particles not in direct contact with the donor surface and insufficient to entrain particles which are in direct contact with the donor surface, so that the particle coating that is left adhering to the donor surface, after each passage through the coating station, is substantially only a single particle deep.