JPH0644694Y2 - On-demand type inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Utilization of the Invention] The present invention relates to an on-demand type ink jet head which ejects ink particles for printing only during recording.

[Background of the invention]

FIG. 7 shows a conventional on-demand type inkjet head. Printing is performed by applying a pulse voltage to the piezoelectric element 31 to deform the partition wall 30 and ejecting a part of the ink in the ink chamber 32 from the orifice 35 as ink particles.

In such an on-demand type inkjet head,
There was a problem that the printing speed was slow. As a solution to this problem, there is a multi-nozzle system in which 20 or more nozzles are mounted in one head. However, if the number of nozzles is increased, the drive control circuit is increased accordingly, so it is a good idea to keep the number of nozzles to a minimum. Another solution is to increase the driving frequency of the nozzle. However, in the basic form as shown in FIG. 7, stable ink particle ejection was initially performed only up to a frequency around 1 kHz. FIG. 8 and FIG. 9 show an example for improving the driving frequency. FIG. 8 shows that the ink supply passage 46 is provided near the orifice 45 and the ink passage 47 is opened to the atmosphere to stabilize the ink supply. FIG. 9 shows that the vibration of the orifice 55 is stabilized and the driving frequency is improved by dividing a part of the ink chamber 53 and dividing the ink chamber into a pressure chamber 52 and a front chamber 54. Both have some effects, but it seems that the limit is about 3 kHz. Further, since the velocity of the ink particles does not increase sufficiently, there is a drawback that the flight direction of the ink particles is deviated due to the influence of the ink film attached around the orifice.

[Purpose of device]

An object of the present invention is to provide an on-demand type ink jet head which eliminates the above-mentioned drawbacks of the prior art, increases the speed and drive frequency of ink particles, and can eject ink particles without satellites.

[Outline of device]

The present invention focuses on the fact that the ink jet head can be driven at a high frequency by promptly suppressing the pressure vibration at the tip of the orifice, and devises the arrangement and structure of the ink path around the orifice.

[Example of device]

FIG. 1 is a partially sectional perspective view showing an embodiment of the head 1 of the present invention. At least one of the two flat plates 10 constituting the head main body has an ink chamber composed of a pressure chamber 2, a contraction channel 3 and a second chamber 4, an ink supply port 12 connected to an ink tank (not shown), and the ink supply port. An ink flow path 6 connecting the pressure chamber 2 to the pressure chamber 2, an orifice 5 located in front of the second chamber 4, a rear end connected to the ink supply port 12, and a front end opened to the atmosphere through an opening 8. Bypass path 7, communication path 9 connecting the ink bypass path 7 and the front of the second chamber 4
Etc. are provided, and these pressure plates 2 to communication passages 9 are formed by bonding the two flat plates 10 together.

A piezoelectric element 11 is attached to the flat plate 10 above the pressure chamber 2 by, for example, an epoxy adhesive or thermocompression bonding. The second chamber 4 communicates with the orifice 5 by reducing the cross-sectional area at an arbitrary opening angle or reducing the cross-sectional area in a stepwise manner. The communication passage 9 connects the fan-shaped portion at the tip of the second chamber 4 near the orifice 5 and the ink bypass passage 7.
It is provided at an acute angle with respect to the perpendicular of the surface of the orifice 5.

At the time of non-ejection, all ink chambers and all ink paths connected from the ink supply port 12 to the orifice 5 and the atmospheric opening 8 are sufficiently filled with ink without inclusion of bubbles or the like.
At the tip portion and the atmosphere opening portion 8, due to the balance of the meniscus, the ink does not overflow from the surface of the orifice 5 and the atmosphere opening portion 8 and, on the contrary, does not take in air bubbles and maintains the equilibrium state.

When the piezoelectric element 11 is driven during ejection, the volume of the pressure chamber 2 is rapidly reduced and a part of the ink therein is ejected from the orifice 5 as ink particles, and then returns to the equilibrium state.
When the pressure chamber 2 is compressed and reduced, the ink chamber on the orifice 5 side of the pressure chamber 2 and the ink passage generally have a streamline in the direction of the orifice 5. Conversely, the pressure chamber 2 is in a state of equilibrium (or expansion) from a compressed state. ), The streamline is from the orifice 5 toward the pressure chamber 2. On the other hand, the ink in the communication passage 9 and the ink bypass passage 7 flows into the communication passage 9 and the ink bypass passage 7 from the pressure chamber 2 when the volume of the pressure chamber 2 is decreasing. This ink flow is due to the effect of the expansion pipe flowing from the narrow communication passage 9 into the large-volume ink bypass passage 7 and the effect of the pressure smoothing of the atmospheric opening 8 provided at one end of the ink bypass passage 7 to the orifice 5 portion. It helps stabilize the surrounding vibrations early.

Next, the influence of the mounting angle θ of the communication passage 9 that connects the orifice 5 portion and the ink bypass passage 7 will be described. FIG. 4 is a view in which the communication passage 9 is attached to the orifice portion and the ink bypass passage 7 at the attachment angle θ. When the relationship between the mounting angle θ of the communication passage 9 and the frequency was measured, it was found that the frequency increased as the mounting angle θ decreased as shown in FIG. However, if the mounting angle θ is too small, the communication passage 9
Is longer and the expansion tube effect of the ink bypass passage 7 cannot be sufficiently exhibited, so the mounting angle is optimally 90 degrees or less, preferably around 30 degrees.

The above results are summarized in FIGS. 2 and 3. FIG. 2 is a frequency characteristic of the conventional head shown in FIG.
In the frequency characteristic of Figure 3 is the present invention the head, at the same frequency f _1, the voltage width V _2> V ₁ (a voltage width, a limit voltage and ink droplets ink particles stably injected as a single ink particles This is the difference from the threshold voltage at which injection is attempted at a speed of almost zero). The effect of widening the voltage range is the ink bypass path 7.
It has been obtained from the measurement experiment that it is due to the atmospheric opening 8 provided in the. Further, the frequency at which a predetermined voltage width V ₀ (voltage width required to obtain a predetermined ink particle velocity) is also f ₂ (frequency under the condition that V ₃ ≧ V ₀ ), which is a head compatible with higher frequencies than conventional heads. Becomes

Figure 6 illustrates another embodiment of the present invention the ink jet head 20 is obtained by forming by stacking a plurality of stainless steel plates 21 ₁ through 21 _k. These stainless steel plates 21 have holes (not shown) at appropriate positions, and when stacked, the pressure chamber 2
2, contraction chamber 23, second chamber 24, orifice 25, ink supply path 2
7. Atmosphere opening 28, communication passage 29, etc. are configured. The piezoelectric element 11 is mounted parallel to the surface of the orifice 25. As shown by the broken line, if the second ink supply path 26 that connects the pressure chamber 22 and the ink supply path 27 is formed,
It has almost the same structure as the head in the figure.

If the second supply passage 26 is not provided, the ink supply to the orifice 25 must be performed through the communication passage 29, and the communication passage 29
It is necessary to increase the cross-sectional area of the orifice 25. However, if the cross-sectional area is increased, there is a problem that the vibration damping of the orifice 25 part is delayed and it is not possible to support high frequency drive. There is a problem that air bubbles are taken in from the part and cavitation occurs. However, if the mounting angle of the communication passage 29 is reduced, vibration damping can be accelerated even if the cross-sectional area of the communication passage 29 is increased.

[Effect of device]

As described above, according to the present invention, by providing the ink bypass paths whose front and rear ends are connected to the atmospheric opening and the ink supply port, respectively, it is possible to quickly suppress the pressure vibration at the tip of the orifice. You will be able to drive.
As a result, it becomes possible to provide an inkjet printer capable of high-speed printing.

[Brief description of drawings]

FIG. 1 is a partially sectional perspective view showing an embodiment of the head of the present invention, FIGS. 2 and 3 are graphs showing frequency characteristics of a conventional head and a head of the present invention, and FIG. 4 is a mounting angle of a communication passage. FIG. 5 is an enlarged view showing FIG. 5, FIG. 5 is a graph showing the relationship between mounting angle and frequency, FIG. 6 is a sectional view showing another embodiment of the head of the present invention, and FIGS. 7 to 9 are sectional views showing an example of a conventional head. It is a figure. In the figure, 1 is an ink jet head, 2 is a pressure chamber, 3 is a contraction chamber, 4 is a second chamber, 5 is an orifice, 6 is an ink supply passage, 7 is an ink bypass passage, 8 is an atmosphere opening portion,
Reference numeral 9 is a communication passage, 10 is a flat plate, 11 is a piezoelectric element, and 12 is an ink supply port.

Claims (2)

[Scope of utility model registration request] 1. An ink supply port to which ink is supplied from an ink tank, an ink chamber in which ink is supplied from the ink supply port through an ink supply path and is filled with ink, and an ink in the ink chamber. An on-demand type ink jet head having an ink particle ejecting means for ejecting a part of the ink particles as ink particles and an orifice for ejecting the ink particles, which is provided in front of the ink chamber. And an ink bypass passage connected to the ink supply port, and a communication passage connecting the ink bypass passage and the vicinity of the orifice, and the communication passage is provided with a shaft connecting the orifice and the ink chamber. An on-demand type inkjet head, which is mounted at an acute mounting angle with respect to the perpendicular of the orifice surface. 2. The on-demand type ink jet head according to claim 1, wherein the mounting angle is approximately 30 degrees.