Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-01-28
2003-02-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S061000
Reexamination Certificate
active
06520626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid ejection head, a method for preventing accidental non-eject using the ejection head and a manufacturing method of the ejection head, and more particularly, a liquid ejection head for ejecting extremely minute liquid droplets.
2. Description of the Related Art
The ink-jet printing system is known as a system for ejecting liquid such as ink used currently. This ink-jet printing system includes a method using electrothermal converting element (heater) as eject energy generating element for ejecting ink droplet and a method using piezoelectric element, and both methods permit to control the ejection of the ink droplet by means of an electric signal.
For instance, the principle of an ink droplet ejection method using the electrothermal converting element consists in boiling ink instantly in the proximity of the electrothermal converting element by delivering an electric signal to the electrothermal converting element, and rapidly ejecting ink droplets by a sudden bubble growth caused by the phase change of the ink at that time. The principle of the ink droplet ejection method using the piezoelectric element consists in changing the piezoelectric element by delivering an electric signal to the piezoelectric element, and ejecting ink droplets by the pressure caused at the time of this displacement of the piezoelectric element.
A system for ejecting liquid by communicating formed bubbles with the atmosphere is known as a liquid ejection method using the electrothermal converting element. The practical application of this system is disclosed in European Patent Publication No. 0454155. The invention described in such patent publication is made by pursuing the cause of splash caused by bubble explosion or unstable droplet formation and concerns a liquid ejection method comprising the steps of generating a bubble in a liquid passage by a temperature elevation suddenly exceeding the core boiling by delivering thermal energy to the liquid passage and communicating the bubble with the atmosphere near the ejection opening of the liquid passage. In such a liquid ejection method of atmosphere communication from the viewpoint of uniformity during bubble growth and bubble communication with the atmosphere, a so-called side shooter structure liquid ejection head, wherein the ejection opening is disposed in a position opposed to the electrothermal converting element is preferable for stable liquid ejection.
BACKGROUND OF THE ART
In such an ink-jet printing system, a still higher image quality, a higher resolution and a higher printing speed are required.
However, in the high quality image formation using the side shooter structure liquid ejection head mentioned above, it was found that the communication property between a bubble and the atmosphere begins to affect droplet ejecting direction according to the volume decrease of droplet to be ejected. Particularly, when the ejected liquid volume is reduced to 20×10
−15
m
3
or less, the trailing (liquid connecting the liquid passage with the main droplet of liquid droplet) and satellite droplet formed by this trailing affect the image quality, and moreover, atomized ink attaches to the surface to be recorded of the printing media and decreases the printing quality, creating a new problem.
The Applicant proposes an excellent ejecting method for resolving the new problem mentioned above using the liquid eject method by the atmosphere communication method. The method is excellent in that it allows one to achieve a high image quality printing with less ejection slippage, by ejecting liquid by communicating a bubble with the atmosphere for the first time in the bubble volume reduction stage, in the so-called side shooter structure liquid ejection head. The inventors have studied to achieve higher resolution and higher quality printing, and found that it is desirable to realize a constantly stable ejection by the ejection method mentioned above, against variable factors such as foaming variation under a high driving frequency, or proprietary variation of nozzles arising in the manufacturing stage. As the result of the empirical analysis of the liquid ejection method mentioned above, the inventors have newly found that in an ejection method wherein liquid is ejected in the defoaming step, it is important to stabilize the liquid movement against variable factors in the whole head arrangement, including not only the ejection opening surface, but also the ejection opening portion forming the ejection opening including the ejection opening surface, and further the eject means and the liquid passage.
The inventors did research on arrangements for suppressing slippage in the droplet ejecting direction, in particular those involving the ejection opening shape, and discovered Japanese Patent Application Laid-open No. 4-39049 (1992). The Patent Publication describes an arrangement wherein the opening section is petal-shaped, in a developer ejection apparatus having a opening section for ejecting developer, a means for ejecting developer from the opening section and a passage where developer flows. However, this Patent Application recognizes as problems that “an extremely unstable behavior occurs during the developer eject due to a distinct boundary between opening sections and non-opening sections of a circular nozzle”, and that “a trajectory flexion occurs due to the entrainment by developer attached to the outer periphery of the circular nozzle at the moment when the developer is ejected”. In other words, it only intends to make uniform the adhesiveness of the ejection opening surface, and does not satisfy the intent of the present invention mentioned above that consists in considering the cause of ejection slippage, including the ejection means and the liquid passage.
Especially, among liquid ejection heads of the side shooter type, in a composition wherein the liquid passage between the ejection opening and the heat resistance element is surrounded by a wall surface forming the passage sidewall except the direction toward the liquid chamber (refer to FIGS.
69
-
72
), bubbles happen to stagnate for some reason in the corner of a volume surrounded by the wall surface forming the passage sidewall. As the result of absorption of the ejecting power at the moment of foaming by this bubble stagnation, liquid ejection may become unstable, ejection speed lower, ejection flow smaller and ejection direction deviated.
If the opening area of the ejection opening of the liquid ejection head is reduced, for realizing a higher image quality and a higher resolution as mentioned above, ejection may be obstructed by an ink droplet attached to the ejection opening surface for some reason. In particular, in the liquid ejection head using the atmosphere communication system mentioned above, a non-eject (called accidental non-eject hereinafter) occurs when the ejection opening is obstructed by an ink droplet, and a white line may appear during the image formation, because that ejection opening does not engage in the printing.
The Inventors have also examined in detail the phenomena mentioned above, and found that the accidental non-eject is a phenomenon of a single ejection opening, and once a non-eject state occurs, it is hard to recover from it if suction or other recovery means are not used.
Moreover, the inventors have obtained new findings that the whole head arrangement including not only the ejection opening surface, but also the ejection opening portion forming the ejection opening including the ejection opening surface, and further ejecting means and liquid passage is important, to such bubble stagnation or accidental non-eject, too.
SUMMARY OF THE INVENTION
The present invention, devised as the result of devoted study by the inventors has a main object to provide a liquid ejection head, allowing one to realize a globally excellent liquid ejection that can meet requirements such as still higher image quality, higher resolution and higher printing speed, by taking into
Barlow John
Canon Kabushiki Kaisha
Do An H.
Fitzpatrick ,Cella, Harper & Scinto
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