In general, inkjet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto recording media or onto an image receiving member surface. A phase-change inkjet printer employs phase-change inks that are in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. A mounted printhead ejects drops of the molten ink to form an ink image. The ink can be ejected directly onto print media or onto an image receiving member surface, such as a rotating drum or moving belt, before the image is transferred to print media. Once the ejected ink is transferred to the print medium the ink droplets quickly solidify to form an image.
The media used in both direct and offset printers are typically provided in sheet or web form. A media sheet printer typically includes a supply drawer that houses a stack of media sheets. A feeder removes a sheet of media from the supply and directs the sheet along a feed path past a printhead so the printhead ejects ink directly onto the sheet. In offset sheet printers, a media sheet travels along the feed path to a nip formed between the rotating imaging member and a transfix roller. The pressure and heat in the nip transfer the ink image from the imaging member to the media. In a web printer, a continuous supply of media, typically provided in a media roll, is entrained onto rollers that are driven by motors. The motors and rollers pull the web from the supply roll through the printer to a take-up roll. As the media web passes through a print zone opposite the printhead or heads of the printer, the printheads eject ink onto the web. Along the feed path, tension bars or other rollers remove slack from the web so the web remains taut without breaking.
Printers can conduct various maintenance operations to ensure that the ink ejectors in each printhead operate efficiently. A cleaning operation is one such maintenance operation. The cleaning process removes particles or other contaminants that interfere with printing operations from the printhead, and unclogs solidified ink or contaminants from inkjet ejectors. During a cleaning operation, the printheads purge ink through some or all of the ink ejectors in the printhead. The purged ink flows through the ejectors and down the front face of the printheads, where the ink drips into an ink receptacle. To control the flow of ink down the face of each printhead, some printhead assemblies include a drip bib positioned below each printhead. The drip bib has a shape that directs liquid ink toward the ink receptacle. The lower edge of the drip bib tapers to one or more channels or points where ink collects prior to dripping into the receptacle. In some printers, a wiper engages the front face of the printhead and wipes excess purged ink in a downward direction toward the drip bib to remove excess purged ink.
While existing cleaning processes are useful to maintain printheads, removing residual purged ink from the drip bib presents a challenge. Due to surface tension, a small portion of the purged ink that flows down the drip bib remains in contact with the drip bib after the cleaning process. Existing drip bibs include a coating of a low surface energy material, such as polytetrafluoroethylene, to reduce the adhesion between the ink and the drip bib, but small amounts of ink remain on the drip bib after the cleaning process is completed. In inkjet printers using a phase-change ink, this residual ink may cool and solidify while on the drip bib. Occasionally, the solidified ink breaks free from the drip bib and interferes with imaging operations. When the solidified ink separates from the drip bib, the ink may contact the web as the web moves past printheads in the print zone. The solidified ink may negatively affect image quality on the web, and the web may carry the solidified ink past one or more printheads in the print zone. Since printheads are often positioned a short distance from the web, the carried ink may contact the face of one or more printheads with adverse consequences. Thus, improved printhead cleaning is desirable.