Apparatus for coating a surface with particles

A method of applying a layer of particles to a receiving surface, which method comprises:

• i) providing an application chamber partially bounded by the receiving surface;
• ii) utilizing an air source to blow an air stream into the application chamber;
• iii) returning air from the application chamber to an intake of the air source to form an air circulation loop;
• iv) introducing into the air circulation loop particles to be coated onto the receiving surface, and
• v) controlling the rate of introduction of particles into the air circulation loop so as to maintain the particle concentration within predetermined limits, the rate of introduction of particles being in response to measuring the centration of particles in the air circulation loop.

An offset printing system comprising an intermediate transfer member (ITM), a coating apparatus for applying a layer of particles to the ITM, an imaging station for applying energy to selected particles on the ITM to render the particles transferrable to a substrate, and an impression station at which only particles to which energy is applied in the imaging station are transferred from the ITM to a substrate to form an image on the substrate, wherein the coating apparatus comprises:

• a) an application chamber partially bounded by the receiving surface, the application chamber being surrounded by a bell housing defining a suction chamber for preventing particles from escaping into the ambient atmosphere;
• b) a source of pressurized air in fluid coupling with the application chamber;
• c) an air return path forming fluid communication between the application chamber and an intake of the air source, the return path forming a portion of an air circulation loop;
• d) a dosing device coupled to a source of particles to be coated onto the receiving surface and capable of controllably introducing measured amounts of the particles into the air circulation loop, and
• e) a controller electrically coupled to the dosing device and controlling the dosing device to dynamically maintain the particle concentration in the application chamber within predetermined limits;
• and
• wherein the system further comprises an optical device for viewing the image transferred to the substrate, and an output image processor configured to analyze image data from the optical device, the controller of the coating apparatus serving to regulate the dosing device in dependence upon a signal from the output image processor.

An offset printing system comprising an intermediate transfer member (ITM), a coating apparatus for applying a layer of particles to the ITM, an imaging station for applying energy to particles on the ITM selected in response to a signal received from an input image processor to render the particles transferrable to a substrate, and an impression station at which only particles to which energy is applied in the imaging station are transferred from the ITM to a substrate to form an image on the substrate, wherein the coating apparatus comprises:

• a) an application chamber partially bounded by the receiving surface, the application chamber being surrounded by a bell housing defining a suction chamber for preventing particles from escaping into the ambient atmosphere;
• b) a source of pressurized air in fluid coupling with the application chamber;
• c) an air return path forming fluid communication between the application chamber and an intake of the air source, the return path forming a portion of an air circulation loop;
• d) a dosing device coupled to a source of particles to be coated onto the receiving surface and capable of controllably introducing measured amounts of the particles into the air circulation loop, and
• e) a controller electrically coupled to the dosing device and controlling the dosing device to dynamically maintain the particle concentration in the application chamber within predetermined limits;
• and,
• wherein the controller of the coating apparatus serves to regulate the dosing device in dependence upon a signal from the input image processor.