JPH07266556A - Ink jet head - Google Patents

Abstract

PURPOSE:To prevent bubbles from residing in an ink channel. CONSTITUTION:An ink channel having a nozzle 7 that ejects ink at the front end thereof and a common ink chamber 3 communicating with the ink channel are formed on the top side of a substrate 1. The ink channel is comprised of a rear ink channel 4, a pressure chamber 5 and a front ink channel 6. The ink channels 4, 6 become shallow toward a nozzle 7 from the pressure chamber and toward the ink chamber 3 from the pressure chamber 5, inclining continuously at an angle of 10 deg. or less. Ink flows smoothly along the moderately inclined stepless surface of the ink channels 4, 6 from the common chamber 3 to the nozzle 7 through the rear ink channel 4, pressure chamber 5, and the front ink channel 6 during the initial operation process of filling ink in the ink channels and bubbles contained in residual ink in the ink channels seldom reside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head.

[0002]

2. Description of the Related Art Generally, an ink jet head is provided with an ink channel having a pressure chamber and a nozzle by etching on a flat glass substrate and a common ink chamber communicating with the ink channel. A thin diaphragm with high rigidity is fixed on top. A piezoelectric element is attached to the upper surface of the diaphragm facing the pressure chamber. The ink supplied to the common ink chamber at a predetermined pressure is supplied to the pressure chamber through the ink flow path. When a voltage is applied to the piezoelectric element here, it deforms due to the electrostriction phenomenon, imparts energy to the ink in the pressure chamber through the vibrating plate, pushes the ink from the pressure chamber into the ink flow path, and directs it from the nozzle to the outside. It is designed to be ejected.

In the above structure, the ink to which the energy is applied in the pressure chamber is sent toward the nozzle and at the same time flows back toward the common ink chamber. So problem 1
One is how to eject a large amount of ink at high speed and efficiently from a nozzle, and another problem is how to rapidly supply ink from a common ink chamber to a pressure chamber.

As an improved technique for solving this, among the ink flow passages before and after the pressure chamber, the communication portion (restriction portion) between the common ink chamber and the ink flow passage and the nozzle portion are
There is one that is formed shallower by providing a step with respect to other flow path portions.

[0005]

In the above-mentioned conventional improved technique, the backflow of the ink is prevented during the printing operation, so that the response frequency is improved. On the other hand, when the ink flow path is filled with ink from the common ink chamber at the time of starting the inkjet head, bubbles remaining in the flow path or mixed in the ink stay in the step portion. Further, when the meniscus generated by the negative pressure is restored, air bubbles may be taken in from the tip of the nozzle, but the air bubbles stay in the step portion. Due to the presence of the air bubbles, the pressing force to be transmitted from the piezoelectric element to the ink is reduced, and accordingly, the efficiency of ink ejection is reduced, the printing speed is reduced, and printing may be impossible.

Therefore, an object of the present invention is to prevent air bubbles from staying in the ink flow path and prevent a decrease in ink ejection efficiency.

[0007]

In order to achieve the above-mentioned object, an ink jet head of the present invention comprises an ink flow path having a nozzle for ejecting ink at its tip, and a common ink chamber communicating with this ink flow path. A pressure chamber provided in the ink flow path, and a pressurizing means for changing the volume of the pressure chamber, the ink flow path from the pressure chamber to the nozzle direction, and from the pressure chamber to the common ink chamber direction, Each is characterized by being inclined at an inclination angle of 10 ° or less and becoming shallower.

[0008]

In the priming of the initial operation, the ink filled in the ink flow path from the common ink chamber smoothly flows along the gently inclined surface having no step in the ink flow path. Further, when the meniscus generated by the negative pressure after the printing operation is restored, the ink that has been on standby smoothly flows in along the gently sloped surface having no step in the ink flow path.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the basic configuration of the ink jet head in this embodiment is similar to that of the prior art, and a channel is formed by etching or the like on the upper surface of a glass plate or a synthetic resin plate having a thickness of 1 to 3 mm. The groove is formed to form the flow path substrate 1. A diaphragm 2 made of a glass plate having a thickness of 0.2 mm is bonded to the upper surface of the flow path substrate 1. A common ink chamber 3 for storing ink, a rear ink flow path 4, a pressure chamber 5, a front ink flow path 6 and a nozzle 7 for ejecting ink are formed between them. Piezoelectric elements 8 are mounted on the upper surface of the diaphragm 2 at positions facing the pressure chambers 5. A portion of the rear ink channel 4 that communicates with the common ink chamber 3 is a restriction portion 4a.

The bottom surface of the front ink flow path 6 is continuously inclined from the pressure chamber 5 to the nozzle 7 at an inclination angle of 10 ° or less to be shallow. Similarly, the bottom surface of the rear ink flow path 4 extends from the pressure chamber 5 to the restriction portion 4a by 10
It is continuously inclined and shallowed at an inclination angle of less than °.

In order to determine this inclination angle, the following experiment was conducted beforehand. That is, an ink jet head was constructed in which the inclination angle of the ink flow path was variously changed, and an initial operation of filling ink in every corner of the ink flow path was performed for each ink jet head. As an example, when the nozzle 7 is covered with a cap and the cap is brought into a vacuum state by interlocking with a vacuum pump, the common ink chamber 3 is removed from an ink tank (not shown).
The ink is sucked into the nozzle, the ink flows out from the nozzle 7 through the rear ink flow path 4, the pressure chamber 5, and the front ink flow path 6, and the ink is filled in all the flow paths. Percentage of bubbles remaining in the ink during this priming (defective rate) (%)
Is the vertical axis, and the inclination angle of the ink flow path is the horizontal axis. As a result of repeated experiments, as shown in FIG. 3, the rear ink passage 4 and the front ink passage 6 communicating with the pressure chamber 5 are continuously inclined from the pressure chamber 5 at an inclination angle of 10 ° or less. It was found that the rate of air bubbles staying was significantly reduced when the water was inclined at a shallow angle. From this result, an inclination angle of 10 ° or less was adopted in the present invention.

Next, when a voltage is applied to the piezoelectric element 8 during the printing operation, the piezoelectric element 8 is deformed, and the diaphragm 2 located on the opposite surface of the pressure chamber 5 is also deformed accordingly. The volume of the pressure chamber 5 is instantly changed. Due to this instantaneous change in volume, pressure energy is applied to the ink filled in the pressure chamber 5, the ink in the pressure chamber is pushed out to the front and rear ink flow paths 4 and 6, and is accumulated in the ink flow path. It works to push the ink out in sequence. At this time, the restrictor portion 4a functions to increase the fluid loss coefficient and prevent the ink, which is pressurized in the pressure chamber 5, from flowing back. On the other hand, since the ink pushed out to the nozzle 7 side has the flow passage resistance reduced by the inclined surface of the front ink flow passage 6 which becomes shallower toward the nozzle side, it is pushed out smoothly to the nozzle side, Is jetted from. When the vibrating plate 2 returns to its original position at the end of ejection, negative pressure is now generated in the pressure chamber 5, and the ink waiting in the common ink chamber 3 passes through the rear ink flow path 4 and pressure chamber. 5 is filled.

Further, due to the negative pressure generated in the pressurizing chamber 5 at the time when the ejection is completed, the ink in the front ink flow path 6 is forced to flow in the pressurizing chamber 5.
However, since the front ink flow path 6 is inclined without a step from the pressure chamber 5 to the tip of the nozzle 7, bubbles are generated as in the conventional case. Even when the ink is taken into the ink, it does not stay in the step portion and cause the ink ejection failure.

As a method for providing the pressure chamber 5 and the inclined surfaces of the front and rear ink flow paths 4 and 6 in the flow path substrate 1, the etching characteristic that the narrow portion has a lower etching rate than the wide portion is utilized. Therefore, as shown in FIG.
The width of the restriction portion 4a is narrowed, and the flow path from the nozzle 7 to the pressure chamber 5 and the flow path from the restriction portion 4a to the pressure chamber 5 are designed to be continuously wide. As a result, as shown in FIG. 1, it is possible to form a portion having a wide width, a portion having a narrow width, a portion having a narrow width, and a portion having a continuously narrow width, a depth having a continuous depth as well by a single etching. In FIG. 2, the width of the opening of the nozzle 7 is 10 to
If the width of the front ink passage port 5a of the pressure chamber 5 is 300 to 500 μm, the depth of the nozzle 7 is about 50 μm.
The depth of the pressure chamber 5 is approx.
m can be etched at the same time.

[0015]

As described above, according to the present invention, when the ink is filled from the common ink chamber to every corner of the ink flow path,
The proportion of bubbles remaining in the ink flow path or mixed in the ink is reduced. In addition, the bubbles taken from the nozzles due to the negative pressure after the ink is discharged are less likely to stay in the ink flow path.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a plan view showing a state where the diaphragm of FIG. 1 is removed.

FIG. 3 is a graph showing a relationship between a defect rate and an inclination angle of an ink flow path.

[Explanation of symbols]

 3 Common ink chamber 5 Pressure chamber 4,6 Ink flow path 7 Nozzle 8 Pressurizing means (piezoelectric element)

Claims (1)

[Claims] 1. An ink flow path having a nozzle for ejecting ink at a tip, a common ink chamber communicating with the ink flow path, a pressure chamber provided in the ink flow path, and a volume of the pressure chamber. And a pressure means for changing the ink flow path, the ink flow path from the pressure chamber to the nozzle direction,
And an ink jet head which is inclined from the pressure chamber toward the common ink chamber at an inclination angle of 10 ° or less and is shallow.