JP2001301165A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head which has a good printing quality and a high response speed. SOLUTION: In this ink jet head 1 of an electrostatic driving type, the center of an ink nozzle 11a with respect to the center of a second nozzle 11b is set to a position of the side where ink is relatively supplied. Even when discrete ink chambers 5 are formed by anisotropic etching to a crystal face orientation (110) silicon, ink liquid drops are discharged straight in a vertical direction to a nozzle face 3a. The ink jet head of the good printing quality and the high response speed can be realized accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a face-ejection type ink jet head in which the angle between a stream line in an individual ink chamber and an ink droplet ejected from an ink nozzle is substantially a right angle.

[0002]

2. Description of the Related Art Conventionally, many ink jet heads have been proposed as represented by JP-B-53-12138 and JP-B-53-45698. The hole shape of the nozzle portion of these inkjet heads was a truncated cone or a cylinder as shown in FIG.

[0003]

However, in these embodiments, the crystal plane orientation (11
When an individual ink chamber is created by anisotropic etching in silicon of 0), and a nozzle portion is arranged at a position facing the inclined surface constituting the individual ink chamber, streamlines are formed along the inclined surface constituting the individual ink chamber. In this case, the streamline could not be made vertical to the nozzle surface in the nozzle portion. As a result, there has been a problem that the ink droplets are not ejected straight in the direction perpendicular to the nozzle surface, and the desired print quality cannot be satisfied.

On the other hand, when an individual ink chamber is formed by anisotropic etching on silicon having a crystal plane orientation of (110), and a nozzle portion is arranged at a position that does not face an inclined surface constituting the individual ink chamber, the ink tank is moved from an ink tank or the like. Since the inflowing air bubbles stay at the position of the tip of the inclined surface, the air bubbles could not be removed. For this reason, there is a problem that a sufficient pressure necessary for discharging in the individual ink chamber cannot be generated, and a desired print quality cannot be satisfied.

On the other hand, if the length of the nozzle portion is increased in order to eject ink droplets straight, the meniscus return speed is reduced due to an increase in flow path resistance in the nozzle portion, There is also a problem that the response frequency of the inkjet head does not improve.

An object of the present invention is to provide an ink jet head having good printing quality and high response speed by devising the structure of the nozzle portion in view of this point.

[0007]

In order to solve the above-mentioned problems, the present invention has an ink nozzle, a second nozzle, and an individual ink chamber, and an individual ink chamber due to a change in volume of the individual ink chamber. In the ink jet head which ejects ink droplets from the ink nozzles by bending the streamline to a substantially right angle, the center of the ink nozzle with respect to the center of the second nozzle is located on the side where ink is supplied relatively. And

Further, the individual ink chambers are formed by anisotropic etching of silicon having a crystal plane orientation of (110).

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrostatically driven ink jet head to which the present invention is applied will be described with reference to the drawings.

FIG. 1 is a sectional view of an electrostatic drive type ink jet head of this embodiment. The inkjet head 1 has a nozzle substrate 3 made of silicon on the upper side with a cavity substrate 2 interposed therebetween.
Are laminated, and a glass electrode substrate 4 is laminated on the lower side to form a three-layer structure.

The central cavity substrate 2 is a silicon substrate having a crystal plane orientation of (110), and is etched from its surface to form a plurality of independent elongated individual ink chambers 5, one common ink chamber 6, Grooves each functioning as a plurality of ink supply ports 7 that connect the common ink chamber 6 to each individual ink chamber 5 are formed.
These grooves are closed by the nozzle substrate 3 to define the respective portions 5, 6, and 7.

An ink inlet 12 is formed in a portion defining the lower surface of the common ink chamber 6. Ink is supplied from an external ink tank (not shown) to the common ink chamber 6 through the ink intake port 12, and from here to the independent individual ink chamber 5 through each ink supply port 7. You.

A nozzle portion 11 is formed on the nozzle substrate 3 at a position corresponding to the front end portion of each individual ink chamber 5, that is, at a position opposite to the ink supply port 7. The nozzle section 11 communicates with the corresponding individual ink chamber 5. On the bottom surface of the individual ink chamber 5, there is provided a diaphragm 51 which is thin and elastically displaceable in an out-of-plane direction (vertical direction in the figure)
Is formed.

On the upper surface of the electrode substrate 4 joined to the cavity substrate 2, a position facing each diaphragm 51 is provided.
A shallowly etched recess 41 is formed. The individual electrode 1 facing the diaphragm 51 is provided on the bottom surface of the concave portion 41.
0 is formed. The individual electrode 10 has a segment electrode portion 10a made of ITO and an electrode terminal portion 10b exposed to the outside.

By joining the electrode substrate 4 to the cavity substrate 2, the diaphragm 51 defining the bottom surface of each individual ink chamber 5 and the segment electrode portion 10a of the individual electrode 10 face each other with a very small gap. . This gap is the sealant 60
And sealed.

The cavity substrate 2 has common electrode terminals 22
Is formed, and a driving voltage is applied between the electrode and each individual electrode 10 by the voltage applying means 21. Since the cavity substrate 2 is conductive, each diaphragm 51 functions as a common electrode.

The vibration plate 51 serving as a common electrode and the individual electrode 10
When the diaphragm 51 is attracted to the individual electrode side by an electrostatic force generated by applying a drive voltage during the period, the diaphragm 51 is elastically deformed and bent toward the segment electrode 10a,
It adsorbs on the surface of the segment electrode 10a. As a result, the volume of the individual ink chamber 5 increases, and ink flows into the individual ink chamber 5 from the side of the common ink chamber 6 via the ink supply port 7.

When the electrostatic attraction force is released, the diaphragm 51 is separated from the surface of the segment electrode 10a by the elastic return force and returns to the initial state. As a result, the volume of the individual ink chamber 5 decreases rapidly. A part of the ink in the individual ink chamber is ejected from the nozzle unit 11 as ink droplets by the ink pressure vibration in the individual ink chamber generated at this time.

(Nozzle Section and Individual Ink Chamber) FIG. 2 (a)
FIG. 2 is a top view mainly showing the nozzle portion 11 of the nozzle substrate 3 and the individual ink chamber 5 of the cavity substrate 2, and FIG. 2B is a partial cross-sectional view taken along line bb.

As shown in these figures, the individual ink chambers 5
Are bottom surface 51a, side wall surface 52, side wall surface 53, inclined surface 54,
It is sectioned by the inclined surface 55. The bottom surface 51a and the inclined surface 54 intersect at an entry corner 56, and the inclined surface 54 and the surface of the cavity substrate 2 intersect at an entry corner 57 and an entry corner 58. As is well known, in the case of etching single crystal silicon with an alkali such as an aqueous solution of potassium hydroxide or hydrazine, anisotropic etching becomes possible because of a large difference in etching rate depending on the crystal plane.

More specifically, since the etching rate of the (111) crystal plane is the lowest, (1)
11) A structure in which the surface remains as a smooth surface is obtained. The side wall surface 52, the side wall surface 53, the inclined surface 54, and the inclined surface 55 are (11
The side wall surface 52 and the side wall surface 53 are perpendicular to the surface of the cavity substrate 2, and include an angle Θ4 of the inclined surface 54 with respect to the cavity substrate 2 and an inclined surface 55 with respect to the cavity substrate 2. Are both 30 °. The angle Θ1 between the entry corner 57 and the side wall surface 52, the angle Θ2 between the entry corner 56 and the side wall surface 52 are both about 125 °, and the angle Θ3 between the entry corner 58 and the side wall surface 53 is about 109 °.

As shown by the dotted line in FIG.
By extending 8 to the side wall surface 52, the entering corner 57 can be eliminated, and by extending the entering corner 57 to the side wall surface 53, the entering corner 58 can be eliminated.

On the side of the nozzle substrate 3, an inclined surface 54
The second part etched into a cylindrical shape
The nozzle 11b is formed, and the center of the second nozzle 11b is
The distance between the entry corner 57, the entry corner 58, the side wall surface 52, and the side wall surface 53 is substantially equal. The ink nozzle 11a has a cylindrical shape with a diameter smaller than that of the second nozzle, and its center is formed at a position where ink is supplied to the center of the second nozzle (the side of the ink supply port 7). is there.

Here, the flow of ink will be described with reference to FIG. Due to the elastic displacement of the vibration plate 51, streamlines indicated by arrows are generated in the ink chamber 5 as shown in the figure. This streamline becomes a streamline of about 15 ° along the slope on the slope 54 (see # 6 in the figure) and reaches near the second nozzle 11b. In order for ink droplets ejected from the ink nozzle 11a to be ejected straight to the nozzle surface 3a in the vertical direction, the second nozzle 11b and the ink nozzle 11a
A streamline of about 15 ° along the inclined surface needs to be in a direction perpendicular to the nozzle surface 3a in the same manner as the discharge direction.
That is, the second nozzle 11b and the ink nozzle 11a
It is necessary to make 90 ° with respect to the stream line of the individual ink chamber.

FIG. 3 is a partial sectional view showing the center of the ink nozzle 11a and the second nozzle 11b in FIG. 2 (b).
The eccentricity with the center of 1a is different. With reference to FIG. 3, the eccentric amount and the ejection direction of the ink droplet 13 will be described. FIG. 3A shows a case where the center of the ink nozzle 11a and the center of the second nozzle 11b are the same. in this case,
Since the streamline along the inclined surface 54 constituting the individual ink chamber 5 reaches the vicinity of the second nozzle 11b, the second nozzle 11
The streamline between b and the ink nozzle 11a is as shown in the figure, and cannot be vertical to the nozzle surface 3a. In fact, according to experiments by the present inventors, the diameter of the ink nozzle 11a is 25 μm, the length is 25 μm, the diameter of the second nozzle 11b is 66 μm, the length is 55 μm, and the center of the second nozzle 11b and the ink nozzle When the center of 11a was the same, the ink droplet was ejected at an angle of about 2 ° to the side opposite to the supply port 7 with respect to the vertical direction of the nozzle surface 3a, as shown at 13a.

FIG. 3B shows the center of the ink nozzle 11a with respect to the center of the second nozzle 11b on the side of the supply port 7.
This is the case where the eccentricity is μm. According to the experiments by the present inventors, for example, the diameter of the ink nozzle 11a is 25 μm, the length is 25 μm, the diameter of the second nozzle 11b is 66 μm, the length is 55 μm, and the ink is positioned at the center of the second nozzle 11b. When the center of the nozzle 11a was eccentric to the side of the supply port 7 by 3 μm, it was confirmed that the ink droplet was ejected in the vertical direction of the nozzle surface 3a as shown by 13b in FIG. As described above, the inclined surface 54 forming the individual ink chamber 5
Along the stream, reaching the vicinity of the second nozzle 11b
With the nozzle 11b and the ink nozzle 11a, it was possible to set the direction perpendicular to the nozzle surface 3a.

That is, as described above, the ejection direction of the ink droplet changes depending on the amount of eccentricity between the center of the second nozzle 11b and the center of the ink nozzle 11a.
Experiments have confirmed that it is suitable to decenter the center of the ink nozzle 11a by 3 μm toward the ink supply port 7 with respect to the center of 1b.

According to experiments by the present inventors, for example, the diameter of the ink nozzle 11a is 25 μm, the length is 100 μm,
In the case where the diameter of the second nozzle 11b is 66 μm and the length is 55 μm, even if the center of the second nozzle 11b and the center of the ink nozzle 11a are the same, the ink droplets ejected from the ink nozzle 11a remain on the nozzle surface 3a. On the other hand, it was confirmed that the liquid was discharged straight in the vertical direction. However, the meniscus return speed decreases due to an increase in the flow path resistance at the nozzle portion, and as a result, the response frequency of the inkjet head decreases, and the inkjet head is not suitable for an inkjet head.

According to experiments by the present inventors, for example, a second nozzle 11b is formed at a position facing the diaphragm 51,
When the center of the ink nozzle 11a was set to the center of the second nozzle 11b, it was confirmed that the ink droplets ejected from the ink nozzle 11a were ejected straight in the vertical direction to the nozzle surface 3a. However, air bubbles flowing from an ink tank or the like stay at positions near the entrance corner 57 and the entrance corner 58 (see FIG. 2A), and thus the air bubbles cannot be removed. As a result, a sufficient pressure required for discharging in the individual ink chamber cannot be generated, and the desired print quality cannot be satisfied.

In the present embodiment, the center of the ink nozzle 11a is decentered by 3 μm toward the ink supply port 7 with respect to the center of the second nozzle 11b. However, the present invention is not limited to this. , The length of the second nozzle, the depth of the individual ink chamber, etc. Further, the ink nozzle 11a and the second nozzle 11b
Has a circular cross-section, but it can be appropriately selected, for example, a polygon such as a triangle or a quadrangle, or a star.

(Modified Example of Nozzle Section) FIG.
Another example of 1 is shown. In FIG. 4A, the second nozzle 11b is formed in a truncated cone, and the ink nozzle 11a is formed in a cylindrical shape.

In FIG. 4B, the second nozzle 11b is formed in a truncated cone, and the ink nozzle 11a is formed in a truncated cone.

FIG. 4C is a partial plan view centering on the nozzle portion 11, and FIG. 4D is a partial cross-sectional view taken along a line cc of FIG. As shown in these figures,
The second nozzle 11b is formed in a truncated square pyramid, and the ink nozzle 1
1a is formed in a cylindrical shape.

The shape of the ink nozzle 11a to be formed, the shape of the second nozzle 11b, the combination of the shape of the ink nozzle 11a and the shape of the second nozzle 11b, etc. have properties that should be appropriately set according to each ink jet head. It is. Therefore, the shape of the ink nozzle 11a, the second nozzle 1
The shape of 1b is not limited to a cylinder, a truncated cone, or a truncated quadrangular pyramid. A truncated pyramid such as a polygon or a star can be appropriately selected.

(Other Embodiments) Each of the above embodiments relates to an electrostatically driven ink jet head.
The present invention can be similarly applied to a piezoelectric inkjet head and an inkjet head using thermal energy.

[0036]

As described above, in the ink jet head of the present invention, the center of the ink nozzle is formed at a position on the side to which ink is supplied relative to the center of the second nozzle. In this manner, even if the individual ink chambers are formed on silicon having the crystal plane orientation (110) by anisotropic etching, an ink jet head having good print quality and high response speed can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electrostatic drive type inkjet head to which the present invention is applied.

FIGS. 2A and 2B are a partial top view and a partial cross-sectional view illustrating a nozzle portion and an individual ink chamber in FIG.

FIG. 3 is a partial cross-sectional view for explaining a discharge direction of ink droplets in FIG.

FIG. 4 is an explanatory diagram showing another configuration example of the nozzle unit in FIG. 1;

FIG. 5 is a top view and a cross-sectional view of a nozzle portion of a conventional inkjet recording apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 inkjet head 2 cavity substrate 3 nozzle substrate 4 electrode substrate 5 individual ink chamber 6 common ink chamber 7 ink supply port 11 nozzle 11a ink nozzle 11b second nozzle 51 diaphragm 52, 53 side wall 54, 55 inclined surface 56, 57, 58 corner

Claims (3)

[Claims] 1. An ink nozzle having a nozzle, a second nozzle, and an individual ink chamber, wherein an ink droplet is ejected from the ink nozzle by bending a streamline of the individual ink chamber due to a change in volume of the individual ink chamber to a substantially right angle. An ink jet head according to claim 1, wherein a center of said ink nozzle is relatively located on a side to which ink is supplied with respect to a center of said second nozzle. 2. The ink jet head according to claim 1, wherein the individual ink chamber is formed by anisotropic etching of silicon having a crystal plane orientation of (110). 3. The individual ink chamber according to claim 1, wherein a volume change is generated in the individual ink chamber by an electrostatic force generated by applying a voltage between the opposing electrodes, and An electrostatically driven ink jet head for discharging ink droplets.