Apparatus for raised printing

#The present invention relates to thermography or raised printing, and in particular to methods and apparatus for applying heat to printed sheets.

#Thermography, or raised printing, is carried out by applying a thermography powder, such as a resin based powder, to a printed sheet while the ink is still tacky. Sufficient heat is applied to melt the powder, whereupon the powder expands and thus imparts a "raised" effect to the printed areas.

#Thermography apparatus which has heretofore been employed for carrying-out raised printing operations has usually included a feeder section into which the printed paper sheets are fed. Resinous powder, e.g., a nylon resin, is applied to the printed surface and adheres to the stilltacky ink. Thereafter, excess powder is shaken or sucked from the sheet, leaving powder on the ink only. The sheets are then placed onto a conveyor belt which conveys the sheets through a heat tunnel, with the printed side facing upwardly. An overhead heater, such as an electric resistance heater, heats the sheets and powder to the melting temperature of the powder as the sheets travel through the heating tunnel. As the powder melts, it expands and thus "raises" the printing. Thereafter, the conveyor may conduct the sheets through a cooling tunnel where cooling air is blown against the sheets to solidify the raised print.

#The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof, in connection with the accompanying drawings in which like numerals designate like elements, and in which:

#FIG. 1 is a perspective view of a raised printing machine according to the present invention;

#FIG. 2 is a longitudinal sectional view through a sheet heating section, the section being taken along line 2--2 of FIG. 3;

#A thermography machine 10 according to the present invention comprises a frame 12 which supports a sheet infeed section 14, a powder pick-up section 16, a heating section 18, a cooling section 20, and a discharge section 22.

#The paper infeed section is conventional and includes one or more driven belts 24 which feeds sheets one-at-a-time to a second belt arrangement 26 (a discharge end of the belt arrangement 26 depicted in FIG. 2), the latter feeding the sheets through the powder pickup section 16. The powder pickup section 16 includes a conventional hopper 28 which applies a thermography powder, e.g., a nylon resin based powder, onto the upwardly facing ink-printed surface of each sheet. The powder must be applied while the ink is still in a tacky state so that the powder adheres to the ink.

#Excess powder is sucked from the sheet and belt by a conventional vacuum pickup unit 30 which delivers the powder to a conventional powder separator 32. The separator removes the powder from the air and recirculates that powder back to the hopper.