Recording element and recording device

Details Recording element and recording device Recording element and recording device

1997-07-21

2002-01-08

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S054000, C347S068000

Reexamination Certificate

active

06336707

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording element for ejecting drops of liquid such as ink drops to a surface to be printed, and a recording device which uses such element.
2. Description of the Related Art
A typical recording method for printing by ejecting drops of liquid, more specifically ink drops onto a surface to be printed uses nozzles. The nozzle type recording method to the date includes “on-demand” type and “continuous flow” type.
The on-demand type recording is a method that prints by ejecting ink intermittently from nozzles in response to recording information, exemplary types of this method include “piezoelectric vibrator” type and “thermal” type. The piezoelectric vibrator type operates, by applying pulsed voltage to the piezoelectric elements disposed in vicinity of ink chamber to distort it, for varying the liquid pressure of the ink in the ink chamber to eject ink drops from the nozzles to perform recording of dots on a recording medium paper. And the thermal type on-demand recording operates, by heating ink with a heater element provided in the ink chamber to form bubbles thereby to eject ink drops from nozzles to perform recording of dots on a recording medium.
On the other hand, in the continuous flow type, some pressure is applied to the ink to eject continuously from the nozzle, while at the same time vibration is applied by a vibrator such as the piezoelectric element to cause the projected ink column to be liquid drops, and charging and deflecting are selectively performed to the ink drops for recording.
FIG. 21
shows the overview of the piezoelectric vibrator type printing: a nozzle
72
is provided in one side of an ink chamber
71
, while a piezoelectric element
73
is provided outside in the opposite side, and ink
74
is fulfilled in the ink chamber
71
. By applying voltage to the piezoelectric element
73
, which deforms such that its volume within the ink chamber
71
is to be minimized, to thereby increase the pressure in the ink chamber
71
to eject ink from the nozzle
72
. In such printing method the diameter of the ejected ink drops will be determined mainly by the diameter of the nozzle
72
.
FIG. 22
shows the overview of the thermal type printing: a nozzle
82
is provided in one side of an ink chamber
81
, while a heater element
83
is provided within the ink chamber
81
, and ink
84
is fulfilled in the ink chamber
81
. By applying voltage to the heater element
83
to heat the heater element
83
, ink nearby the heater element
83
is caused to be heated to form bubbles, to thereby increase the pressure in the ink chamber
81
to eject ink from the nozzle
82
. In this method, similar to the piezoelectric vibrator type printing, the diameter of the ejected ink drops will be determined mainly by the diameter of the nozzle
82
.
SUMMARY OF THE INVENTION
The resolution of the image to be printed in a variety of recording type had been required to be 300 dots per inch (dpi) in the prior art; recently, higher resolution such as 600 to 720 dpi has been required. In order to satisfy such a demand, the diameter of the dot on a recording medium paper has to be smaller, this follows that the diameter of the nozzle has to be smaller such that the diameter of the ink drops ejected become smaller.
However, when the diameter of the nozzle become smaller, blocking of nozzles by particles or dust, blocking of nozzles by dried ink surface in the nozzle, and further the change of the ink ejection direction by sticked ink sludge in the circumference of the nozzle may occur easily and some defects of the printing quality on the recording medium may be resulted. Therefore the diameter of the nozzle may not be small enough to the size needed to form a dot size corresponding to the required resolution.
There have been proposed some recording method for recording by ejecting ink drops onto the surface to be printed by using vibration or acoustic wave instead of nozzle in order to overcome such problems as cited above.
The first of the recording method without using nozzles in the prior art, as disclosed in the U.S. Pat. No. 4,308,547, is the printing method in which a piezoelectric element shell with concaved spherical surface is disposed in the ink, and voltage is applied thereto via electrodes. In this method, longitudinal longitudinal wave radiated from the piezoelectric element shell to the ink is concentrated to a point in a ink free surface for ejecting drops from the ink free surface.
Moreover, a similar type of printing as disclosed in the Japanese Published Examined Patent Application No. Hei 6-45233 as a method for improving the productivity and the fine structured precision, is the one in which a spherical concaved recess is provided on a substrate such as glass to form an acoustic lens, and a vibrator comprised of a piezoelectric element and electrodes for applying voltage to the piezoelectric element is formed on the other side of the substrate, then the vibrator is disposed in the ink. In this method, as similar to the method disclosed in the above cited U.S. Patent, the vibration from the vibrator is emitted as longitudinal wave in the ink, concentrated into a point on the ink free surface by means of the concaved acoustic lens for ejecting drops from the ink free surface.
In the Japanese Published Unexamined Patent Application No. Hei 3-200199, a method is disclosed in which a phased Fresnel lens in the form of thin film plate is provided on a substrate for a focusing lens less expensive but sharper. The phased Fresnel lens operates as a lens that plane incident wave is diffracted at a plurality of thin film plate disposed annularly spaced apart at a distance, then a plurality of radiated diffracted waves are combined in a point on the ink free surface to become maximum amplitude.
As mentioned above, the first of the recording method without using nozzles converges the vibration emitted from the vibrator into one point on the ink free surface to eject ink drops. The acoustic lens is made by forming a lens by the piezoelectric element itself, or by using a phased Fresnel lens for overlaying the same phase, or by using concaved lens. It should be noted that in the acoustic lens, since the relationship between the lens form and the convergence and divergence of wave is the reverse of that of the optical lens, a concaved lens should be used; the wave will be diverged with a convex lens.
Here, the diameter of ejected drop is approximately equal to the diameter of the converged bundle when longitudinal waves propagated in the ink are converged onto the ink free surface, and the converged diameter “d” will be d~F/f, where “f” is the driving frequency of the vibrator, “F” is the aperture value (F value) of the lens. The relation between the wavelength of the longitudinal waves propagated in the ink “&lgr;” and its propagation speed “v” and the driving frequency “f” of the vibrator will be: v=f·&lgr;.
Thus, when for example, very fine ink drops of the drop diameter of approximately 15 micron is to be ejected, if the F value of the lens is 1, then the prior propagation speed of the longitudinal wave in the low viscosity water-based ink is approximately 1500 meters/sec., thus the driving frequency of the vibrator has to be set to a very high frequency such as approximately 100 MHz. Since the F value of the lens is, in practice, quite difficult to be significantly small due to many problems, in general, for the drop diameter “d” to be smaller, the vibrator is to be driven at a higher frequency.
As mentioned above, in the first printing method without nozzles as a plurality of vibrators have to be driven at a high frequency of near 100 MHz, a cost-related problem that the driving means becomes expensive may be resulted in, while other significant problems such as the change of the drop diameter by the variation of the ink viscosity due to the heating, or the blocking of ink ejection by the dried or solidified ink itself within a recording element, may occur.
The heating may be caused

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