JP2001130025A - Ink jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To release from the designing of a fluid passage wherein a flowing speed of ink at an irregular portion such as a nozzle in an ink pressurizing chamber is to be greater than that at the other portion in order to allow a bubble attached to the irregular portion to flow therefrom. SOLUTION: A pressure wave of which the frequency is greater than that of ink ejection is applied to a portion in the vicinity of a nozzle so that the ink flow for guiding bubbles at the portion to a pressurizing chamber is created thereby removing the bubbles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink jet recording head, and more particularly to the removal of air bubbles from a pressure chamber.

[0002]

2. Description of the Related Art In an ink jet recording head, pressure is generated in an ink pressure chamber by some method, and ink droplets are ejected from nozzles and adhere to a recording medium. Recording is performed in this manner. At this time, if bubbles are present in the ink pressure chamber, the ink ejection characteristics are affected to a considerable extent.

[0003] There is a method of removing the existing air bubbles by flushing the ink with a steady flow of ink. In the flushing method, pressure is constantly applied from an ink supply passage to generate an ink flow toward an ink discharge passage. At that time, in order to flush out the bubbles adhering to the irregularities such as the nozzles in the ink pressure chamber, the flow velocity must be increased, or the flow path must be designed so that the ink flow velocity increases in the irregularities. Was.

In some cases, bubbles existing near the nozzles are removed by discharging the bubbles together with the ink from the nozzles.

[0005]

However, in order to design a flow path so that air bubbles remaining in an uneven portion are swept away, the shape of the flow path greatly affects the discharge characteristics such as the discharge speed and discharge amount of ink. Discharge performance must be sacrificed. Also,
When discharging air bubbles from the nozzles, the discharged ink is wasted, or even if such ink is collected, a device such as an ink reservoir must be newly added.

That is, an object of the present invention is to remove bubbles by a steady ink flow by moving bubbles adhering to the concave and convex portions so that the ink is not wasted or a simple mechanism is used. Another object of the present invention is to discharge ink droplets with stable characteristics without sacrificing the discharge characteristics at the time of design.

[0007]

According to the present invention, there is provided an ink jet recording head having a nozzle communicating with an ink pressure chamber, and pressure generating means for discharging ink from the ink pressure chamber from the nozzle. The method is characterized in that a high-frequency pressure wave higher than the frequency of ink ejection is applied to the vicinity of the nozzle to generate an ink flow that guides bubbles near the nozzle to the pressure chamber to remove the bubbles. Further, the high-frequency pressure wave is generated by using a pressure generating means for discharging ink.

[0008]

FIG. 1 is a longitudinal sectional view of one embodiment of an ink jet recording head of the present invention. The ink droplets are pushed out of the ink pressure chamber 3 through the nozzle 2 on the nozzle plate 1 and are discharged. The pressure for discharging is generated from the vibrator 4. The vibrator 4 is composed of a piezoelectric element layer of several tens of μm and an electrode of several μm, and the electrodes are formed on the comb teeth alternately in positive and negative directions. By making the layers thinner, the required electric field can be obtained at lower driving voltages. Mold material 5 uses silicone resin,
For the purpose of promoting the attenuation of residual vibration and coating the electrodes,
It is provided on the side surface of the vibrator 4. A pressure plate 6 for transmitting pressure is bonded to an end of the vibrator 4, and an elastic film 7 using a polyimide film or the like is bonded to a boundary with the ink pressure chamber 3. Vibrator 4
Is transmitted to the ink via the elastic film 7. When the vibrator 4 is displaced, the pressure plate 6 is displaced in the direction of the nozzle 2, and an ink droplet is ejected from the nozzle 2. The other end of the vibrator 4 is fixed to a substrate (not shown). The base 9 serves to hold each component.

In the ink jet recording head of this embodiment, ink droplets are ejected by driving the vibrator 4 at a voltage of 30 V and a pulse width of 10 μs. The driving frequency is about 12 kHz at the maximum. Here, pressure generating means for discharging bubbles is provided in a pressure generating mechanism including the vibrator 4, the mold material 5, the elastic film 7, and the pressure plate 6, as in the case of discharging ink.

FIG. 2 shows the state of an experiment for removing bubbles. First, FIG. 2A shows a state in which bubbles 8 adhere to the vicinity of the nozzle 2. The bubbles 8 existing in the nozzles 2 are not easily discharged only by a steady flow in the ink pressure chamber 3. Arrow A in the figure indicates the direction of the steady ink flow.

FIG. 2 (b) shows a case where a high-frequency pressure is applied by the pressure generating means (reference numerals 4 to 7) in this embodiment.
4 shows a state in which an ink flow generated in the ink pressure chamber 3 is observed from a discharge direction. An ink flow was observed to occur in the direction indicated by arrow B.

FIG. 2C shows a state in which the bubble 8 moves from the vicinity of the nozzle 2. Experiments have confirmed that the bubbles 8 move from the vicinity of the nozzle portion due to the ink flow generated by applying high-frequency pressure.

FIG. 2D shows a state in which the bubbles 8 are moved by a steady ink flow. By applying pressure using a pump or the like in the direction of arrow A, a steady ink flow is generated, and air bubbles moved from the nozzle portion can be easily pushed away.

In this experiment, the vibrator 4 was driven at a voltage of 10 V and a frequency of 50 kHz for about 0.3 seconds using a heat-meltable ink. Furthermore, when the driving frequency was changed from 50 kHz to 200 kHz, it was also confirmed that the effect of moving bubbles increased as the frequency increased. Further, when the pulse width was set to 3 μs or less, an effect of moving the bubbles without ejection was obtained even when driven at the same driving voltage of 30 V for ejection. Furthermore, even when the driving voltage was lowered from the driving conditions for discharging, the effect of moving bubbles was obtained.

FIG. 3 shows an example of a block diagram of a drive system for an ink jet recording head according to the present invention.
In each of the examples given here, a high-frequency pressure for moving bubbles is generated by using a pressure generating mechanism for discharging ink droplets. Of course, the same effect can be obtained even if a pressure generating mechanism dedicated to bubble movement is provided.

FIG. 3A is a block diagram of a drive system for an ink jet recording head according to the present invention when moving bubbles by setting the pulse width to 3 μs or less. The pulse width can be changed by sending a signal from the control unit to the drive unit.

FIG. 3B is a block diagram of a drive system for an ink jet recording head according to the present invention in a case where bubbles are moved by using a drive voltage different from that during ejection. In this case, a power supply for moving bubbles is required separately from the ejection. In the present embodiment, an ink jet recording head having one nozzle is shown, but this can be applied to an ink jet recording head having a plurality of nozzles.

FIG. 4 is a schematic perspective view of an ink jet recording head having a plurality of nozzles. In this case, there is a method of removing bubbles that is possible because of having a plurality of nozzles.

FIG. 5 illustrates a method of discharging bubbles in an ink jet recording head having a plurality of nozzles. In the plurality of nozzles 2 arranged vertically in FIG. 5, high-frequency pressure is applied sequentially from the nozzles 2 located at the lower portion by the above-described method to move the bubbles 8 upward. By sequentially applying pressure, air bubbles that are moved downward from the uneven portions and reattach to the upper uneven portions can be further moved upward. By sequentially performing high-frequency driving in this manner,
Bubbles 8 are collected at the top of the ink flow path and can be easily removed.

[0020]

As described above, the ink jet recording head of the present invention has a function of applying high-frequency pressure to the vicinity of the nozzle, thereby generating an ink flow from the vicinity of the nozzle to the pressure chamber, thereby forming the ink near the nozzle. Existing bubbles can be moved to facilitate removal of the bubbles.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an ink jet recording head according to the present invention using a pressure mechanism for ejection as a pressure means.

FIG. 2 is a cross-sectional view illustrating a state in which bubbles in an ink pressure chamber of the ink jet recording head of the present invention are discharged.

FIG. 3 is a block diagram of a drive system for an ink jet recording head according to the present invention.

FIG. 4 is a perspective view of an ink jet recording head of the present invention having a plurality of nozzles.

FIG. 5 is a cross-sectional view illustrating a state of a bubble discharging method of the ink jet recording head of the present invention having a plurality of nozzles.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle plate 2 Nozzle 3 Ink pressure chamber 4 Vibrator 5 Mold material 6 Pressure plate 7 Elastic film 8 Bubbles 9 Base Arrow A Direction of steady ink flow Arrow B Direction of ink flow generated by high frequency pressure

Claims (2)

[Claims] 1. A method for removing air bubbles in an ink jet recording head, comprising: a nozzle communicating with an ink pressure chamber; and a pressure generating means for discharging ink from the ink pressure chamber from the nozzle. A bubble removing method for an ink jet recording head, comprising: applying a high-frequency pressure wave higher than a time frequency to generate an ink flow for guiding bubbles near a nozzle to the pressure chamber to remove the bubbles. 2. The method according to claim 1, wherein the high-frequency pressure wave is generated using a pressure generating means for discharging ink.