JPH11157060A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent foams from remaining in a pressure chamber when ink is filled and a nozzle surface is cleaned or the like. SOLUTION: An ink jet head is constituted of a nozzle hole 11 for jetting ink drops, a pressure chamber 5 for applying pressure to ink, a connecting section flow path 12 for connecting the nozzle hole 11 with the pressure chamber 5 and a pressure generating means for generating jet pressure in the pressure chamber 5. The distance L from a top 52 of a wall face 51 of the pressure chamber 5 on the opposite side of an ink jet line 7 in the longitudinal direction of the pressure chamber 5 to the connecting section flow path 12 on the section almost vertical to an ink flow line 14 in the vicinity of a connecting section of the connecting section flow path 12 with the pressure chamber 5 is almost 50 μm or shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an ink jet head, and more particularly, to a technique of discharging air bubbles near a nozzle portion having a rectifying function and rectifying an ink stream line.

[0002]

2. Description of the Related Art In general, an ink jet head has a pressure generating chamber for pressurizing ink to discharge ink droplets, one end of which communicates with an ink tank via an ink supply path, and the other end of which has an ink droplet. Is provided. Then, a part of the pressure generating chamber is formed so as to be easily deformed and used as a vibration plate, and this is elastically displaced by an electromechanical conversion means to generate a pressure for discharging the ink droplet from the nozzle opening.

A recording apparatus using such an ink jet head has excellent features such as low noise and low power consumption.
It is widely used as an output device for an information processing device. Further, with higher performance of information processing devices, higher quality of output characters and images is required, and it is urgently necessary to develop a technology for more stably ejecting fine ink droplets. I have.

In general, an ink jet head has a plurality of nozzles arranged substantially on a straight line, and a recording apparatus using the nozzle relatively moves the ink jet head and the recording paper in a direction substantially orthogonal to the straight line. To output a two-dimensional image. Therefore, in order to achieve high quality by increasing the dot density, the interval between adjacent nozzles (also referred to as nozzle pitch) is reduced, and the difference in the ink droplet flight direction between the nozzle rows arranged in a plurality of rows is reduced. It is necessary to. In addition, it is necessary to reliably eliminate bubbles in the pressure chamber in order to obtain stable ejection.

[0005]

However, each of the above prior arts has the following problems to be solved.

[0006] In an ink jet head using an electrostatic actuator disclosed in Japanese Patent Application Laid-Open No. 8-290567, when ink in a pressure chamber is sucked when ink is filled or when the nozzle surface is cleaned, etc. In some cases, air bubbles sometimes stayed in the region between the slope of the pressure chamber and the nozzle plate. When the bubbles of the ink remain, there is a problem in that a sufficient pressure for ejecting the ink droplet cannot be applied to the ink in the pressure chamber, and the ink droplet cannot be ejected. In addition, it is necessary to suck ink from the nozzle hole side for a long time in order to eliminate the air bubbles that are likely to stay, and the consumption of ink other than that used for printing increases. In addition, there have also been problems such as a longer time required for printing.

Further, as shown in the figure, when the nozzle portion is arranged at a position including the wall surface in the pressure chamber in order to avoid stagnation of bubbles in the pressure chamber, the ink stream lines do not point in a desired direction, There has been a problem that a flight deflection of the ejected ink occurs.

[0008]

In order to solve the above-mentioned problems, an ink jet head according to the present invention comprises a nozzle portion for discharging ink droplets, and a nozzle portion provided in communication with the nozzle for applying pressure to the ink. An ink jet head of a type having a pressure chamber, an ink supply path for supplying ink to the pressure chamber, and pressure generating means for generating a discharge pressure for discharging ink droplets in the pressure chamber, wherein the pressure of the nozzle portion is The opening to the chamber side opens all the way to the pressure chamber side, the nozzle part is composed of a nozzle hole and a plurality of connecting part flow paths, and in a cross section substantially perpendicular to the ink flow line between the nozzle part and the communicating part of the pressure chamber, The apex of the wall surface of the pressure chamber on the side opposite to the ink supply path is located at a distance of 50 μm or less from the nozzle portion. Interruption Cross-sectional area of the relative cross-sectional area of the pressure chamber, it is desirable to reduce gradually in the direction of travel of the ink flow line.

Further, when the nozzle portion is composed of the nozzle hole and one connecting portion flow path, the ratio of the width of the pressure chamber to the width of the connecting portion flow passage is determined by the width of the connecting portion flow passage and the width of the nozzle hole. Desirably, it is approximately equal to the ratio.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Explanation of Operation Principle of Electrostatic Actuator) FIG. 1 is a sectional view of an ink jet head to which the present invention is applied, and FIG. 2 is a plan perspective view thereof.

As shown in these figures, an ink jet head 1 has a silicon substrate 2 sandwiched therebetween, a nozzle plate 3 also made of silicon on the upper side, and a borosilicate glass substrate 4 whose thermal expansion coefficient is close to that of silicon on the lower side. It has a laminated three-layer structure. In the central silicon substrate 2, a plurality of independent pressure chambers 5 and grooves respectively functioning as common ink chambers 6 provided in common with the pressure chambers 5 are formed by etching from the surface thereof (the upper surface in the figure). Have been.

In the nozzle plate 3, a connecting portion flow path 12 and a nozzle hole 11 are formed at positions corresponding to the front end portions of the respective pressure chambers 5, and these communicate with the respective pressure chambers 5. . Further, an ink supply path 7 connected to the common ink chamber 6 is formed at a position corresponding to the rear end side portion of each pressure chamber 5. By closing the plurality of pressure chambers 5 and the common ink chamber 6 of the silicon substrate 2 with the nozzle plate 3,
Each part 5, 6, 7 is sectioned.

The ink is supplied to the common ink chamber 6 from an external ink tank (not shown) through an ink supply port (not shown). The ink supplied to the common ink chamber 6 passes through the ink supply path 7 and passes through the independent pressure chambers 5.
Respectively.

The pressure chamber 5 is formed so as to be thin so that the bottom wall 8 functions as a diaphragm which can be elastically displaced in the vertical direction in FIG. Therefore, the portion of the bottom wall 8 may be referred to as a diaphragm 8 for convenience of the following description.

Next, in the upper surface of the glass substrate 4 which is in contact with the lower surface of the silicon substrate 2, that is, in the bonding surface with the silicon substrate 2, a shallow surface is formed at a position corresponding to each pressure chamber 5 of the silicon substrate 2. An etched recess 9 is formed. Therefore, the bottom wall 8 of each pressure chamber 5 faces the surface 92 of the concave portion 9 of the glass substrate 4 with a very small gap.

Here, the bottom wall 8 of each pressure chamber 5 functions as an electrode for storing a charge. A segment electrode 10 is formed on the concave surface 92 of the glass substrate 4 so as to face the bottom wall 8 of each pressure chamber 5.
The surface of each segment electrode 10 is covered with an insulating layer made of inorganic glass. Thus, the segment electrode 1
0 and the bottom wall 8 of each pressure chamber 5 form opposing electrodes with an insulating layer interposed therebetween.

In order to drive the ink jet head, charging and discharging between these opposing electrodes are performed in accordance with the print signal 21. One output of the print signal 21 is directly connected to each segment electrode 10, and the other output is connected to a common electrode terminal 22 formed on the silicon substrate 2. Since impurities are implanted into the silicon substrate 2 and the silicon substrate 2 itself has conductivity, charges can be supplied from the common electrode terminal 22 to the bottom wall 8. When it is necessary to supply a voltage to the common electrode with a lower electric resistance, for example, a thin film of a conductive material such as gold may be formed on one surface of the silicon substrate by vapor deposition or sputtering.

(Embodiment 1) FIG. 3 is an enlarged plan perspective view of an ink jet head to which the present invention is applied, and FIG. 4 is a sectional view thereof.

The embodiment will be described with reference to FIGS. 3 and 4. In the ink jet head 1 of the present invention, a nozzle hole 11 for discharging ink droplets and a pressure chamber 5 for applying pressure to ink are provided.
Connecting passage 1 connecting nozzle hole 11 and pressure chamber 5
And pressure generating means for generating an ejection pressure for ejecting ink droplets in the pressure chamber 5. Nozzle hole 11
And the pressure chamber 5 of the nozzle portion 13 composed of the connecting portion flow path 12
The openings to the sides are all open to the pressure chamber 5 side. In a section substantially perpendicular to the ink flow line 14 near the communicating portion between the nozzle portion 13 and the pressure chamber 5, the vertex 52 of the wall surface 51 of the pressure chamber 5 opposite to the ink supply path 7 in the longitudinal direction of the pressure chamber 5 is a nozzle. The distance L from the part 13 is at a position of about 50 μm or less.

Conventionally, the distance L is on the order of several tens to one hundred and several tens of μm, and the entry of minute bubbles from the nozzle holes 11 generated by disturbance vibration to the ink jet head and minute bubbles from the ink tank (not shown). In the case where there is, a bubble having a size of about several tens of μm stays near the vertex 52, and the bubble 15 stays still even when ink is sucked from the nozzle hole 11.

In the structure according to the present invention, since the distance L between the vertex 52 and the nozzle portion 13 is smaller than the size of the minute bubble 15, the bubble 1 is located near the vertex 52 immediately below the nozzle portion 13.
Even if the nozzle 5 is provided, when the ink is sucked from the nozzle hole 11, the bubble 15 is removed together with the ink from the nozzle hole 11.

(Embodiment 2) Another embodiment will be described with reference to FIGS. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 5 is an enlarged plan perspective view of the ink jet head to which the first embodiment is applied, and shows processing deviation of the nozzle portion 13 of the nozzle plate 3, processing deviation of the pressure chamber 5 of the silicon substrate 2, and the silicon substrate 2 and the nozzle plate. 3 shows a case where the position shift of No. 3 occurs. FIG. 6 is a sectional view thereof. FIG. 7 is an enlarged plan perspective view of the inkjet head 1 to which the second embodiment is applied.

As shown in FIG. 5, when the processing deviation and the positional deviation are large, an overlapping portion 18 of the silicon substrate 2 and the nozzle portion 13 is generated. When there is the overlapping portion 18, the action of rectifying the ink flow line 16 in the connecting portion flow path 12 in the Z-axis direction in the drawing is reduced, and the ink droplet 19 is shifted from the desired direction (Z-axis direction in the drawing). And the print quality is degraded. Therefore, in order to prevent the above-described problems from occurring, a processing method of the nozzle portion 13, a processing displacement of the pressure chamber 5, and a positional deviation between the silicon substrate 2 and the nozzle plate 3 are suppressed as much as possible, and a processing method with high accuracy is required. Was.

In the second embodiment, as shown in FIG. 7, a chamfered portion 53 is formed at the vertex 52 of the pressure chamber 5 shown in the first embodiment, so that the pressure chamber 5 can be removed even when there is a processing deviation and a positional deviation. The distance L between the new vertex 56 and the nozzle 13 is set to approximately 5
It is possible to eliminate the occurrence of the overlapping portion 18 between the silicon substrate 2 and the nozzle portion 13 which is located at 0 μm or less.
In the modification of the first embodiment, the distances M and N between the center of the nozzle 13 and the opposing walls 54 and 55 forming the pressure chamber 5 can be set to be substantially equal. Even when observed from the X-axis direction in the drawing, there is no deviation from the desired direction (Z-axis direction in the drawing), and the print quality can be further improved.

(Embodiment 3) Another embodiment will be described with reference to FIGS. The same components as those in the first and second embodiments are denoted by the same reference numerals, and the description is omitted. FIG. 8 is an enlarged plan perspective view of the ink jet head. In the nozzle plate 3, the connecting portion flow path 12 and the second connecting portion flow path 20 are provided at positions corresponding to the front end portions of the respective pressure chambers 5. And a nozzle portion 13 composed of a nozzle hole 11, which communicates with each pressure chamber 5. FIG. 9 is a sectional view of FIG.

As shown in FIGS. 8 and 9, the diameter of the hole gradually decreases as the position of the connecting portion flow path 12, the second connecting portion flow path 20, and the nozzle hole 11 increases. When the processing deviation and the positional deviation of the silicon substrate 2 and the nozzle plate 3 are large, the overlapping portion 18 of the silicon substrate 2 and the nozzle portion 13 occurs as in the first embodiment. When the overlapping portion 18 is present, the effect of rectifying the ink streamlines 16 in the connecting portion flow path 12 in the Z-axis direction in the drawing is reduced.
The ink streamline 21 in the second connecting portion flow path 20 is rectified in a desired direction (the Z-axis direction in the figure) by the rectifying action of the ink streamline of FIG. direction)
And the print quality can be improved. Further, as compared with the first embodiment, the hole diameter of the connecting portion flow path 12 can be made larger, so that the possibility of the retention of bubbles is further reduced, and the ejection stability of ink droplets can be further improved.

(Embodiment 4) Another embodiment will be described with reference to FIG. The same components as those in the third embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 10 is a cross-sectional side view in the X-axis direction of FIG. 2 of the inkjet head to which the present embodiment is applied.

The ink jet head 1 of this embodiment has a nozzle hole 11 for discharging ink droplets, a pressure chamber 5 for applying pressure to the ink, and a connecting portion flow path 12 connecting the nozzle hole 11 and the pressure chamber 5. And a second connecting portion flow path 20 and pressure generating means for generating a discharge pressure for discharging ink droplets in the pressure chamber 5. In particular, the width W 1 of the pressure chamber 5 and the connecting portion flow path 12 The ratio P1 of the width W2, the ratio P2 of the width W2 of the connecting portion channel 12 and the width W3 of the second connecting portion channel 20, the width W3 of the second connecting portion channel 20, and the width W4 of the nozzle hole 11 Is substantially equal to the ratio P3.

As described above, the nozzle hole 11 and the connecting portion flow path 1
2. According to the configuration of the nozzle portion 13 by the second connecting portion flow path 20, the cross-sectional shape changes smoothly in the direction of the ink flow line 16 in the connecting portion flow path, and the ink flow also changes rapidly. Instead, it changes gradually and stably. The stable and gradual change of the ink flow also stabilizes the ejection state of the ink droplets and facilitates the discharge of air bubbles in the inkjet head.

When the nozzle portion 13 is constituted only by the nozzle hole 11 and the connecting portion flow path 12, the ratio P1 between the width W1 of the pressure chamber 5 and the width W2 of the connecting portion flow path 12 is determined by the following formula. The same effect can be obtained by setting the ratio W2 to the ratio P2 of the width W2 of the nozzle hole 11 to the width W2 of the nozzle hole 11.

(Modification of the Fourth Embodiment) As shown in FIG. 10, an ink jet head 1 according to a modification of the fourth embodiment has a nozzle hole 11 for discharging ink droplets and a pressure chamber for applying pressure to the ink. 5, a connecting portion flow path 12 and a second connecting portion flow path 20 connecting the nozzle hole 11 and the pressure chamber 5, and pressure generating means for generating a discharge pressure for discharging ink droplets in the pressure chamber 5. In particular, a line 22 connecting the nozzle hole 11, the connecting portion flow path 12, and the pressure chamber 5 is substantially on a straight line. Also in this configuration, similarly to the fourth embodiment, an effect of stably gradually changing the flow of the ink from the connection channel 12 to the nozzle hole 11 can be obtained.

[0032]

In the structure according to the present invention, the pressure chamber 5
Bubbles do not stay in the inside, and it is possible to apply a sufficient pressure to the ink in the pressure chamber to discharge the ink droplet, and it is possible to stably discharge the ink. Further, since the ink suction time required for eliminating bubbles in the pressure chamber is also reduced, it is possible to reduce the consumption of waste ink used for purposes other than printing.

Further, it is not necessary to dispose the nozzle portion at a position including the wall surface in the pressure chamber in order to avoid the stagnation of bubbles in the pressure chamber, and the ink stream line is directed in a desired direction, and the discharge direction of the discharged ink droplet is also changed. Since they substantially coincide with the desired direction, the effect of improving the print quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of an ink jet head of the present invention.

FIG. 2 is a plan perspective view of an embodiment of the inkjet head shown in FIG. 1;

FIG. 3 is a partially enlarged view of an embodiment of the ink jet head shown in FIG.

FIG. 4 is a sectional view of an embodiment of the ink jet head shown in FIG.

FIG. 5 is an enlarged plan perspective view of the embodiment of the ink jet head shown in FIG. 3 when a processing shift occurs.

FIG. 6 is a sectional view of an embodiment of the ink jet head shown in FIG.

FIG. 7 is an enlarged plan perspective view showing another embodiment of the inkjet head of the present invention.

FIG. 8 is an enlarged plan perspective view showing another embodiment of the inkjet head of the present invention.

FIG. 9 is a sectional view of an embodiment of the ink jet head shown in FIG.

10 is a side sectional view in the X-axis direction in FIG. 2 showing another embodiment of the ink jet head of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink-jet head 2 Silicon substrate 3 Nozzle plate 4 Glass substrate 5 Pressure chamber 6 Common ink chamber 7 Ink supply path 8 Vibration plate 9 Depression on glass substrate 10 Segment electrode 11 Nozzle hole 12 Connection part flow path 13 Nozzle part 14 Nozzle part Ink flow line near the communicating part with the pressure chamber 15 Bubbles just below the nozzle part 16 Ink flow line in the connecting part flow path 17 Discharge direction of the discharged ink droplet 18 Overlapping part of the silicon substrate and the connecting part flow path 19 Discharged ink droplet 20 2nd connecting part flow path 21 Ink flow line in the second connecting part flow path 22 Line connecting the nozzle hole, the plurality of connecting part flow paths, and the pressure chambers 51 Wall surface of the pressure chamber 52 Apex of the pressure chamber 53 of the pressure chamber Chamfered part 54 Wall surface of pressure chamber 55 Wall surface of pressure chamber 56 Apex of pressure chamber 92 Surface of concave part of glass chamber

Continued on the front page (72) Inventor Shigeo Nojima 3-3-5 Yamato, Suwa-shi, Nagano Pref. Seiko Epson Corporation

Claims (3)

[Claims] A nozzle for discharging ink droplets;
A pressure chamber provided in communication with the nozzle portion for applying pressure to ink, an ink supply path for supplying ink to the pressure chamber, and a pressure for generating a discharge pressure for discharging ink droplets in the pressure chamber. And an opening to the pressure chamber of the nozzle portion is entirely open to the pressure chamber, and the nozzle portion is constituted by a nozzle hole and a plurality of connecting portion flow paths. In a cross section substantially perpendicular to the ink flow line between the pressure chamber and the communication section of the pressure chamber, the top of the wall of the pressure chamber opposite to the ink supply path has a distance of 5 mm from the nozzle section.
An inkjet head, which is located at a position of 0 μm or less. 2. The ink jet head according to claim 1, wherein a cross-sectional area of the nozzle hole and a cross section of the connecting portion flow path in a section substantially perpendicular to an ink flow line advances with respect to a cross-sectional area of the pressure chamber. An ink jet head characterized by gradually decreasing in a direction. 3. The ink jet head according to claim 1, wherein the nozzle portion includes the nozzle hole and one connecting portion flow path, and a ratio of a width of the pressure chamber to a width of the connecting portion flow path is equal to the width. An ink jet head, wherein the ratio of the width of the connecting portion flow path to the width of the nozzle hole is substantially equal.