Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-10-15
2001-10-23
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06305787
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an ink jet recording method for forming a high quality image which is applicable to printers, LCD color filter manufacturing machines, textile printing machines, printing plate making machines, and the like. More particularly, it relates to a novel ink jet recording method in which ejection of an insulating oily ink is controlled by an electrostatic field under irradiation with light.
BACKGROUND OF THE INVENTION
An image recording apparatus in which small droplets of liquid ink are ejected onto a recording medium to form a dot image has been put to practical use as an ink jet printer. The ink jet printer is attracting attention as a recording means on plain paper for its advantages over other recording means, such as low noise, compactness, and no necessity of development and fixing. Of various ink jet printing systems so far invented, typical are a system comprising ejecting ink droplets under pressure of vapors generated by heat of a heating element (see, for example, JP-B-56-9429 and JP-B-61-59911 (The term “JP-B” used herein means an “unexamined Japanese patent publication”)) and a system comprising ejecting ink droplets by mechanical pulsated pressure generated by a piezoelectric element.
Recording heads practically used in these ink jet printers include a serial scanning type head which is mounted on a carriage and moves in a direction (main scanning direction) perpendicular to the moving direction of recording paper (secondary scanning direction). Because it is difficult to increase the recording speed with this serial scanning type head, a so-called line scanning type head is conceivable, which is as wide as recording paper to achieve an increased recording speed. However, it is not easy to realize such a line scanning type head for the following reasons.
An ink jet recording system essentially suffers from local concentration of ink due to evaporation or volatilization of the solvent, which is apt to cause clogging of individual fine nozzles in conformity to resolving power. Further, the system utilizing pressure of vapors to create an ink jet involves adhesion of insoluble matter due to thermal or chemical reactions between the vapors and the ink, and the system using pressure generated by a piezoelectric element has a complicated structure for ink passage that may boost the likelihood of clogging. A line scanning type head requires several thousands of nozzles, much more than several tens to a hundred and several tens of nozzles as required in a serial scanning type head. Therefore, clogging occurs with fairly high frequency in the line scanning type head to reduce reliability seriously.
Another problem associated with conventional ink jet recording apparatus is inadequacy for improvement of resolving power. That is, the system using the pressure of vapors has difficulty in forming ink droplets of 20 &mgr;m or smaller in diameter. Since ink droplets unavoidably feather on a recording medium, it is difficult for ink droplets greater than 20 &mgr;m to form dots of about 50 &mgr;m or smaller in diameter. On the other hand, because the recording head used in the system utilizing the pressure generated from a piezoelectric element has a complicated structure, there is difficulty of processing in making a head of high resolving power.
In order to overcome these disadvantages, an ink jet recording method involving use of electrostatic force has been proposed, in which a voltage is applied to an array of thin film electrodes to eject ink or a colorant component thereof from the ink liquid surface. Included in this method are a system comprising ejecting ink by electrostatic attraction force (see JP-A-49-62024 and JP-A-56-4467 (The term “JP-A” used herein means an “unexamined published Japanese patent application”)) and a system comprising ejecting ink containing charged colorant particles in an increased concentration (see W093/11866: PCT/AU92/00665).
In these systems a slit nozzle head that does not require a nozzle for every dot or a nozzleless head that does not require a partition for making up an ink channel for every dot is used. Therefore, the systems are effective in preventing or treating clogging that has been a great bar to realization of a line scanning type recording head. According to the latter system, in particular, ink droplets of very small diameter can be formed and ejected stably, and it is colorant particles in ink that is mainly ejected so that the printed material suffers little feathering. The latter system is therefore promising for achieving high resolving power. Conventional ink jet recording apparatus using the system of ejecting colorant particles by electrostatic force comprise, as stated above, a recording head having an array of electrodes, on each of which a high voltage of several hundreds to several thousands of volts is applied to eject ink.
However, in case where such an electrode array is applied to a multi-nozzle head having a plurality of ink ejection nozzles like a line scanning type head, electric field interference between adjacent electrodes gives rise to a problem when a high voltage is fed to the electrodes. Further, the voltage signals for ink ejection are generally sent by on-off control of the output voltage from a high-voltage power source by means of a drive. Where the applied voltage is high, it is necessary to use a high-voltage resistant drive, which increases the price of the apparatus. Although this problem could be solved by reducing the distance between the head and a recording medium to lower the applied voltage, such will make image formation instable, because the printing performance is liable to undergo the influences of the thickness of recording medium, paper dust, or dust in air.
SUMMARY OF THE INVENTION
An object of the invention is to provide an electrostatic type ink jet system which exhibits high resolving power without feathering, operates stably, and is inexpensive and whose line scanning type head is easy to make. More specifically, the object is to reduce the signal voltage for cost reduction and stable operation in an ink jet recording system in which ink containing charged colorant particles is ejected in an increased concentration.
Other objects and effects of the present invention will become apparent from the following description.
The inventor studied, from various aspects, on ink for ink jet recording and an ink jet recording method suitable for the ink. As a result, it has been found that the objects of the invention can be accomplished by the following ink jet recording methods:
(1) An ink jet recording method comprising:
supplying insulating oily ink to an ejection part disposed so as to face a recording medium;
irradiating the ink at said ejection part with light;
applying an electrostatic field to the ink at said ejection part under irradiation in accordance with image data so as to eject the ink to form an image on the recording medium; and
recovering excess ink from said ejection part.
(2) The ink jet recording method according to the above (1), wherein said insulating oily ink comprises:
a nonaqueous solvent having a specific electric resistance of not lower than 10
9
&OHgr;cm and a specific dielectric constant of not higher than 3.5; and
a dispersoid dispersed in said nonaqueous solvent, which comprises at least colored particles that are solid at ordinary room temperature.
(3) The ink jet recording method according to the above (1) or (2), wherein said irradiating light involves a wavelength that is absorbed by said ink.
According to the ink jet recording method of the present invention, an ink dot image can be formed with high resolving power, without suffering ink feathering, in a stable manner and at a low cost. The invention enables easy making of a line scanning type head, which realizes high-speed recording.
REFERENCES:
patent: 3575841 (1971-04-01), Harris
patent: 5975680 (1999-11-01), Wen et al.
patent: 49-62024 (1974-06-01), None
patent: 56-4467 (1981-01-01), None
patent: 56-9429 (1981-03-01), None
patent: 61-59911 (1986-12-0
Ishii Kazuo
Kato Eiichi
Nakazawa Yusuke
Fuji Photo Film Co. , Ltd.
Nguyen Thinh
Reed Smith LLP
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