1. Field of the Invention
The present invention relates to an inkjet printing apparatus and a method of discharging a shipping ink and more particularly to an inkjet printing apparatus and a shipping ink discharging method which discharges the shipping ink from a print head filled with that ink.
2. Description of the Related Art
If, during a long period of storage or during shipping, a print head of an inkjet printing apparatus is left not filled with ink, a film of contaminants coming from surrounding environment may be formed over the surface of heaters in the print head. When in use, such a print head is likely to exhibit deteriorated bubble formation characteristics and therefore a degraded print quality. To prevent such a degradation in the bubble formation performance, a technique has been known to fill the print head with a shipping ink which is a printing ink cleared of coloring components and is used during storage and shipping.
When a print head filled with a shipping ink is used in a printing apparatus for a printing purpose, the print head, before starting a printing operation, undergoes a conventional shipping ink discharging process known as an ageing processing technique (e.g., Japanese Patent Laid-Open No. H05-169676 (1993)). The ageing processing technique involves applying heat pulses successively to heaters of the print head to separate and remove an oxide film and impurities deposited on the heaters, then installing the print head in the printing apparatus, discharging the shipping ink from the nozzles and filling the print head with a printing ink from an ink tank for the printing operation.
However, in a line type print head that is used in printing laboratories where large volumes of prints are processed, the use of the above ageing processing technique in discharging the shipping ink may result in significant amount of the shipping ink remaining in the print head. This is because the line type print head has many nozzles and long flow path connecting these nozzles and therefore a correspondingly large volume of shipping ink required to fill them.
Moreover, simply discharging the shipping ink with a bubble formation energy alone, that is, by means of ink ejection through nozzles activation alone, leaves a significant amount of the shipping ink, that was loaded into the flow path in the print head, undischarged, though the shipping ink in the liquid chamber in the print head can be expelled.
Further, in an inkjet printing apparatus that performs an ink circulation operation through the line type print head, if a shipping ink remains in the print head, it may during the ink circulation operation be mixed with a printing ink present in the printing apparatus body. If an ink mixed with the shipping ink is used for printing on a print medium, it may take long before the printed color or hue becomes stabilized.