This invention relates to a liquid jet recorder for jetting a liquid for forming field liquid drops for recording.
A recorder using heat energy is available as one of liquid jet recorders for jetting a liquid for recording. This thermal liquid jet recorder using heat energy is in the limelight as a recorder which provides high image quality and can execute high-speed recording although it is manufactured at low cost. In the thermal liquid jet recorder, a heating resistor is energized for converting electric energy into heat energy, which then is transmitted to a liquid for film boiling of the liquid and the liquid is jetted by pressure at the growth time of produced bubbles. At this time, as the heating resistor generates heat, a substance consisting essentially of carbon adheres onto a protective film of the heating resistor from the liquid and a film consisting essentially of carbon is deposited on the protective film because of long-term use. This film hinders transmission of heat energy produced from the heating resistor to the liquid, lowering energy efficiency, weakening the liquid jet force, thus causing degradation of the image quality.
On the other hand, a single pulse drive method and a multi-pulse drive method are available as main drive methods of the thermal liquid jet recorders. FIGS. 2A and 2B are illustration of examples of the thermal liquid jet recorder drive methods. The single pulse drive is a drive method for giving one pulse to a heating resistor as shown in FIG. 2A. Formerly, the single pulse drive was used; the multi-pulse drive as shown in FIG. 2B is used as a stabler drive method and becomes mainstream at present. The multi-pulse drive is a drive method for giving multiple pulses for driving a thermal liquid jet recorder. In the example shown in FIG. 2B, first energy is given on pulse P1, called prepulse P1, to the extent that it does not jet a liquid, and the liquid is warmed. After a lapse of pause period P2, energy for jetting the liquid is given on pulse P3, called main pulse P3, for flying liquid drops. However, if the multi-pulse drive is executed, a film consisting essentially of carbon remains deposited on a protective film; the above-described problem is unsolved.
A measure against the problem that a film consisting essentially of carbon is deposited on a protective film of a heating resistor is described, for example, in the Unexamined Japanese Patent Application Publication No. Hei 6-122198, wherein an impact (cavitation) force of ink concentrating on bubble removal points when bubbles are removed is raised by raising ink temperature and lowering ink viscosity for improving the inertia force at the refilling time with ink, by executing multi-pulse drive for warming ink for increasing the number of molecules changing in state from liquid phase to vapor phase, or by halving the drive voltage for increasing the number of phase conversion molecules for peeling off and removing the film of carbon, etc., on the protective film of the heating resistor. Removal of deposit by cavitation is also described in the Unexamined Japanese Patent Application Publication No. Hei 7-17040.
FIGS. 3A to 3C are illustration of state examples on a protective film of a heating resistor after removal of deposit. In the figure, the hatching density denotes the deposit degree; the higher the density, the more the deposit. FIG. 3C shows the state on a protective film of a heating resistor after removal of deposit according to the invention described later; it is desired to remove the deposit as shown here.
According to the method as described in the document, the deposit can be removed on the periphery of the bubble disappearance point as shown in FIG. 3A. However, the area of the deposit that can be removed is not the whole protective film and is only the periphery of the bubble disappearance point; the deposit at points away from the bubble disappearance point cannot completely be removed, as shown in FIG. 3A.
A method of removing the deposit in the area that cannot be removed is described, for example, in the Unexamined Japanese Patent Application Publication No. Hei 8-90790, wherein at least one of prepulse P1 and pause pulse P2 is modulated two steps or more for changing the bubble removal (disappearance) point position. However, the position is not sufficiently changed and deposit remains as shown in FIG. 3B.