US Patent 7762656 Method for preventing nozzle contamination during warm-up

A method of operating a print head comprises heating the print head from a first temperature below a melting temperature of the phase change ink to a second temperature above the melting temperature. The print head has a nozzle plate with plurality of nozzles for ejecting the phase change ink onto an ink receiver. A first pressure is applied to an interior of the print head as the temperature of the print head increases from the first temperature to the second temperature. The first pressure is configured to prevent phase change ink from entering into the print head through the nozzles of the print head. The first pressure is removed from the print head in response to the print head being at approximately the second temperature.