This invention relates to an ink jet printing head, particularly one which eliminates ink stoppages during a printing operation. Many kinds of printing machines have been developed from impact types to non-impact types. Non-impact types include electronic photographic systems, electro-static systems, thermal systems and ink jet systems. The ink jet system is very quiet, low in power consumption and small in size, yet broad use of the ink jet system has not been attained. The main reason is that the ink jet system fails frequently due to a blockage condition within the ink jet nozzle. Therefore, substantial efforts have been made to develop an ink jet nozzle to avoid this problem. Such efforts have not been sufficient to use ink jet systems without the problems mentioned above, whereby sufficient reliability is obtained.
Furthermore, a new type of ink jet printer using a film having a plurality of holes or recesses in which ink is supplied is disclosed in U.S. Pat. No. 4,608,577 issued Aug. 26, 1986. Yet, it is still very difficult to completely print using a plurality of holes within the film since the film floats upon a bubble while ink is sprayed using instantaneous heat of a thermal head. Printing of sufficient density cannot be obtained.
Some of the prior art which addresses this problem is disclosed in U.S. Pat. Nos. 3,747,120, 4,263,601, 4,308,547, 4.312,009, 4,337,467, 4,366,487 and 4,515,487.
Furthermore, Japanese Patent Publication 61-59914 shows an open ended ink jet nozzle. Only a part of the ink in the nozzle is sprayed by a process causing bubbles. Increasing and decreasing the amount of ink bubbles allows printing. When the ink is quickly heated in the nozzle, some bubbles remain. However, if the thermal dot element is heated without ink, the printing head is damaged.