Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-12-23
2002-03-12
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S061000
Reexamination Certificate
active
06354698
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a method for ejecting liquid droplets onto various media, such as a sheet of paper, to record images on the medium. In particular, it relates to a method for ejecting extremely fine liquid droplets.
There are various recording methods which have been put to practical use in various printers or similar apparatuses. Among them, the recording methods which employ the ink jet systems disclosed in the specifications of U.S. Pat. No. 4,723,129, and 4,740,796 are very effective. According to these patents, thermal energy is used to cause so-called “film boiling”, and the bubbles generated by the “film-boiling” are used for ejecting liquid in the form of droplets.
Among the ink jet based recording methods, the one disclosed in the specification of U.S. Pat. No. 4,410,899 has been known as an ink jet system based recording method of a sort that does not block a liquid path while forming a bubble.
The inventions disclosed in the above documents are applicable to various recording apparatuses. However, there is no record that a recording system which allows a bubble that is formed in an ink path to eject liquid, to become connected to the atmospheric air (hereinafter, “bubble-atmospheric air connection system” or simply, “bubble-air connection system”), has been developed enough to be put to practical use.
The conventional “bubble-air integration systems” rely on bubble explosion, but they are not stable in terms of liquid ejection. Therefore, they cannot be put to practical use. However, there is a promising system, which is disclosed in Japanese Laid-Open Patent Application No. 161935/1979. The liquid ejection principle in this system is unclear. According to this system, a cylindrical heater is fitted in a cylindrical nozzle, and the liquid in the nozzle is separated into two portions by the bubble formed in the nozzle. However, this system also has a problem that a large number of ultramicroscopic liquid droplets are generated at the same time as a primary liquid droplet is generated.
The specification of U.S. Pat. No. 4,638,337 also presents a structure of the bubble-air integration system, in its Prior Art section. However, this patent presents this structure, in which a bubble generated in liquid by the thermal energy given by a heat generating element becomes connected to the atmospheric air, as an undesirable example of the liquid ejection head structure in which ink fails to be ejected or ink is ejected in a direction deviating from the predetermined direction.
This phenomenon occurs under a specific abnormal condition. For example, if a bubble, which has been grown by the driving of a heat generating element, ejects liquid at a point in time when the meniscus, which is desired to be located adjacent to the ejection orifice of an ink path (nozzle) at the moment of ink ejection, has just retracted toward the heat generating element, the liquid, or the ink, is ejected in an undesirable manner.
This is evident because this phenomenon is clearly described, as an undesirable example, in the specification of U.S. Pat. No. 4,638,337.
On the other hand, examples of practical application of the bubble-air connection system are disclosed in Japanese Laid-Open Patent Applications Nos. 10940/1992, 10941/1992, 10942/1992 and 12859/1992. These inventions disclosed in Japanese official gazettes resulted from the pursuit of the causes of the generation of the aforementioned liquid splashes or ink splashes by bubble explosion, and the unreliable bubble formation. They are recording methods which comprise a process in which thermal energy is given to the liquid in a liquid path in an amount large enough to cause the liquid temperature to suddenly rise to a point at which so-called “film boiling” of the liquid occurs and a bubble is generated in the liquid in the liquid path, and a process in which the bubble generated in the recording process becomes connected to the atmospheric air.
According to these recording methods, which cause a bubble to become connected to the atmospheric air adjacently to the ejection orifice of the liquid path, liquid can be desirably ejected in response to a recording signal without causing the splashing of liquid or formation of liquid mist, which is liable to occur in the case of a conventional printer or the like, adjacently to ejection orifices.
SUMMARY OF THE INVENTION
From the viewpoint of the uniformity with which a bubble grows and becomes connected with the atmospheric air, in other words, from the viewpoint of reliability in liquid ejection accuracy, the aforementioned bubble-air connection liquid ejection method is desired to be used with a so-called side shooter type liquid ejection head, in which ejection orifices are positioned to directly face corresponding electrothermal transducers.
However, as a liquid droplet ejected from the aforementioned side shooter type liquid ejection head is reduced in volume to form an image of higher quality, the way a bubble becomes connected to the atmospheric air affects the direction in which a liquid droplet is ejected. In particular if the volume of a liquid droplet is reduced to no more than 20×10
−15
m
3
, the trailing portion (portion which connects the primary-droplet-to-be portion to the liquid path), and the satellite liquid droplets generated by the trailing portion, affect image quality. In addition, the smaller the liquid droplet volume, the higher the probability of ultramicroscopic airborne liquid mist being generated, and therefore, the image quality becomes worse due to the adhesion of the liquid mist to the recording surface of a sheet of recording medium.
Thus, the primary object of the present invention is to provide a liquid ejection method that uses a liquid ejection head capable of ejecting extremely small liquid droplets, and in which a bubble connects to the atmospheric air, in such a way that liquid droplets are ejected without deviating from the predetermined ejection direction, thereby accomplishing high quality recording.
Another object of the present invention is to provide a liquid ejection method which does not allow liquid mist to be generated even when liquid droplets are reduced extremely in volume in order to increase image quality.
The present invention was made as an innovative liquid ejection method based on the bubble-air connection system, and was discovered during the research and development carried out to solve the aforementioned problems in the liquid ejection methods based on the bubble-air connection system which had been disclosed earlier. The knowledge acquired by the inventors of the present invention during the research and development carried out in order to accomplish the aforementioned objects are as follows.
The present invention was made by paying attention to the fact that the formation of a bubble by heat is an extremely stable process, but if the volume of a liquid droplet is reduced enough to achieve a high quality image, even an extremely small amount of change to a bubble is not insignificant. Furthermore, a small amount of “wetting” which is caused by ink droplets adjacent to ejection orifices is not insignificant in terms of the direction in which liquid droplets are ejected. Prior to the aforementioned research and development conducted by the inventors of the present invention, attention had been paid only to the process in which a bubble becomes connected to the atmospheric air, whereas the present invention pays attention to a process subsequent to the bubble connecting to the atmospheric air, as well as to the connecting process.
The essence of the present invention, which is based on the above-described knowledge, is as follows.
The present invention is characterized in that in a liquid ejection method, which employs a liquid ejection head comprising electrothermal transducers for generating thermal energy for ejecting liquid, liquid ejection orifices positioned so as to face, one for one, the electrothermal transducers, and liquid paths which lead, one for one, to the
Kaneko Mineo
Tachihara Masayoshi
Barlow John
Mouttet Blaise
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