JPH11291489A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head in which the quantity of ink to be ejected can be varied. SOLUTION: An electrostatic ink jet head 10 comprises a plurality of individual electrodes 36, 38, 40 disposed oppositely to a common electrode 32 while differentiating the interval. Electrostatic force being formed between electrodes is varied by varying the individual electrode to be applied with a voltage and the quantity of ink to be ejected from the ink jet head is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrostatic ink jet head.

[0002]

2. Description of the Related Art Conventionally, a first electrode fixed on a substrate, a second electrode arranged at a distance from the first electrode, a diaphragm supporting the second electrode, and a first electrode. A driving unit that applies a voltage between the electrode and the second electrode,
By applying a voltage (image signal) between the first electrode and the second electrode from the driving unit, the diaphragm is deformed, and the electrostatic ink jet head that pressurizes and discharges ink based on the deformation is provided. Are known.

[0003] The ink ejection force of this electrostatic ink jet head is determined by the electrostatic force (see Equation 1) generated between the first electrode and the second electrode.

[0004]

(Equation 1)

[0005]

According to this equation, when the inter-electrode voltage (V) changes, the electrostatic force changes. Therefore, it is theoretically possible to discharge different amounts of ink by adjusting the voltage between the electrodes. However, changing the inter-electrode voltage requires a plurality of drivers, for example, a low-voltage driver, a medium-voltage driver, and a high-voltage driver. In addition, the price of the driver dramatically increases according to the outputtable voltage, and it is inevitable that the price of the ink jet head will increase. It is also possible to adjust the ink ejection amount by changing the electrode area. However, in a high-density ink jet head, the area difference is not sufficiently reflected on the ink ejection amount.

[0006]

Accordingly, the present invention provides a first electrode fixed on a substrate, a second electrode spaced from the first electrode, and a second electrode fixed to the first electrode. A voltage is applied between the diaphragm supporting the electrodes and the first electrode and the second electrode, whereby the diaphragm is moved based on an electrostatic force generated between the first electrode and the second electrode. A driving unit that deforms, based on the deformation of the diaphragm, an electrostatic ink jet head that pressurizes and discharges ink contained in the vicinity of the diaphragm, wherein the first electrode or the second electrode At least one of the plurality of partial electrodes is separated from each other, and the distance between each of the first and second electrodes, which is the other electrode, and each of the partial electrodes is different from each other.

In another aspect of the ink jet head according to the present invention, the plurality of partial electrodes are arranged so as not to overlap each other when viewed from the direction in which the first electrode and the second electrode face each other. .

In another aspect of the ink jet head according to the present invention, each of the plurality of partial electrodes is at least partially formed with another electrode when viewed from the direction in which the first electrode and the second electrode face each other. They are arranged to overlap. In this case, an insulating layer is interposed between the partial electrodes that are overlapped with each other.

[0009]

In the ink jet head according to the present invention, the first electrode or the second electrode is composed of a plurality of partial electrodes, and the distance between these partial electrodes and the other electrode is small. Each is different. Therefore, by changing the number of partial electrodes to which a voltage is applied, the electrostatic force formed between the first electrode and the second electrode changes, and the amount of ink ejected from the inkjet head changes. Therefore, if each partial electrode is connected to a power supply that outputs the same voltage via a switching circuit, the amount of ink to be ejected can be changed only by selecting a partial electrode to which a voltage is applied by this switching circuit. As a result, even with an ink jet head having nozzles arranged at a high density, the ink ejection amount can be varied only with an inexpensive low voltage driver.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show an inkjet head 10 according to one embodiment. This inkjet head 10 has three substrates, namely, a first substrate 12,
It is configured by laminating a second substrate 14 and a third substrate 16. These three substrates 12, 14, and 16 can be formed of a resin such as silicon, photosensitive glass, nickel, polyimide having excellent ink resistance, and polysulfone. In the present embodiment, the substrate 12 is made of borosilicate glass. The substrate 14 is formed of silicon and the substrate 16 is formed of borosilicate glass, and is bonded to the adjacent substrates by anodic bonding.

The second substrate 14 has a surface facing the first substrate 12 processed by anisotropic etching to form a plurality of depressions capable of accommodating the ink 20, as shown in detail in FIG. That is, the plurality of ink chambers 22, the ink discharge nozzles 24 connecting the ink chambers 22 to the atmosphere, and the ink chambers 2
Refill chamber 2 containing the ink 20 to be refilled
6, and an ink supply path 28 connecting each ink chamber 22 to the ink supply chamber 26 is formed, whereby the bottom wall of the ink chamber 22 is formed as a thin (thickness: about 3 μm) diaphragm 30. Further, the second substrate 14 adjacent to the third substrate 16
The surface of is formed by boron ion implantation and diffusion to form a boron doping layer (common electrode 32). When a boron doping layer is formed first and then the ink chamber 22 is formed by etching, the boron doping layer functions as an etching stop layer.

The third substrate 16 has a surface facing the second substrate 14, and an insulating space 34 is formed in each region facing the diaphragm 30. The depth of the insulating space 34 is set so as to gradually increase from the front where the nozzle 24 is located toward the opposite side.
8 and 40 are formed, and the distance from the diaphragm 30 to each of the steps 36, 38 and 40 is gradually increased. Each of the step portions 36, 38, and 40 is provided with an individual electrode (partial electrode) 4 using a film forming technique described below.
2, 44, and 46 are formed respectively, and these individual electrodes 4
The intervals between 2, 44, 46 and the diaphragm 30 are set to 0.4 μm, 0.45 μm, and 0.5 μm, respectively.

Each of the individual electrodes 42, 44 and 46 is covered with an insulating film 48 made of an insulating material such as SiN and having a thickness of about 0.1 μm. In FIG. 1, the insulating film 48 is omitted to display each individual electrode. Each individual electrode 42, 4
4 and 46 are also conductive lead portions 56, 58 and 60 (FIG. 4).
(See FIG. 3), and is connected to a switching circuit 62. The switching circuit 62 allows a constant voltage to be individually applied to each of the individual electrodes 42, 44, 46. The switching circuit 62 also
It is connected to the common electrode 32 described above. This switching circuit 62 is further connected to a drive circuit 64,
The driving circuit 64 outputs an image signal to the switching circuit 62.

When the ink 20 is ejected using the ink jet head 10 configured as described above, the driving circuit 6
4 outputs an image signal to the switching circuit 62.
This image signal includes a signal for instructing ejection of the ink 20,
A signal for instructing which of the individual electrodes 42, 44, 46 to apply a voltage to is included. The switching circuit 62 selects the individual electrode 42, 44 or 46 to which a voltage is to be applied from the latter signal, and applies a voltage between the common electrode 32 and the selected individual electrode 42, 44 or 46. As a result, an electrostatic force is generated between the common electrode 32 and the selected individual electrode 42, 44 or 46, and the thin diaphragm 30 supporting the common electrode 32 is applied to the selected individual electrode 42, 44 or 46. Deform toward. At this time, the common electrode 32 and the individual electrode 4
Contact with 2, 44, 46 is prevented. Further, since the relative permittivity of SiN forming the insulating coating 48 is about 20 times that of air, there is an effect of increasing the electrostatic force between the electrodes.

Due to the deformation of the diaphragm 30, a negative pressure is generated in the ink chamber 22, and the ink 20 in the ink supply chamber 26 is supplied to the ink chamber 22 via the ink supply path 28.
Next, when the image signal is turned off, the electrostatic force between the individual electrodes 42, 44 or 46 and the common electrode 32 disappears, and the elastic force of the diaphragm 30 returns to the position before deformation (see FIG. 2). . As a result, the ink 20 in the ink chamber 22 is
Is pressed, and the ink 20 is ejected from the nozzle 24.

As is apparent from the above-described formula 1, the electrostatic force generated between the individual electrode and the common electrode decreases as the distance between these electrodes increases. Therefore, when a constant voltage is applied to each of the individual electrodes 36, 38, and 40 independently, the electrostatic force generated when the voltage is applied to the individual electrode 36 and the displacement amount of the diaphragm 30 due to the electrostatic force are the smallest, and therefore, the ejection is performed. While the amount of ink is the smallest, the electrostatic force generated when a voltage is applied to the individual electrode 40 and the displacement amount of the diaphragm 30 due to the electrostatic force are the largest, and therefore the amount of ink ejected is also the largest. In other words, by applying a voltage to the individual electrode 38 when ejecting an ink droplet of a normal size, and by applying a voltage to 36 or 40 when ejecting an ink droplet having a smaller or larger diameter than this. The image quality of an image to be printed can be variously changed. Further, by combining individual electrodes to which a voltage is applied, the ink ejection amount can be changed in more stages.

Incidentally, a voltage of 40 volts is applied to each individual electrode 3.
When applied to 6, 38, and 40, respectively, the ink ejection amounts in each case were 60 picoliters, 38 picoliters, and 20 picoliters. In addition, the individual electrodes 36
When 40 volts are simultaneously applied to the individual electrodes 38 and 40, the ink ejection amount is 105 picoliters. When 40 volts are simultaneously applied to the individual electrodes 38 and 40, the ink ejection amount is 65 picoliters. 4 at the same time
The amount of ink discharged when 0 volt was applied was 135 picoliters.

Referring to FIG. 4, individual electrodes 4 are
An example of a procedure for forming the wirings 2, 44, 46 and their wirings will be described. As shown in the figure, through holes 50, 52, 54 corresponding to the individual electrodes are formed in the substrate 16 by using a sand blast method. Next, after forming a resist layer on the electrode formation surface of the substrate 16, a region corresponding to the individual electrode 46 is exposed using an appropriate mask (not shown), and the resist layer in the region is removed. The recess 68 is formed by etching. Next, the resist in a region corresponding to the individual electrode 44 is removed and etched to form a dent 70 in this region, and the dent 6 already formed is formed.
Increase the depth of 8. In the same manner, further exposure and etching are repeated to form a depression 72 in a region corresponding to the individual electrode 42, and the depth of the depressions 68 and 70 already formed is increased, whereby the steps 36, 38, and 40 are formed.
To form After that, the individual electrodes 42, 44, 46 are formed on the steps 36, 38, 40, respectively, by using a known film forming technique such as sputtering or CVD. Also, the conductive leads 56, 58, 6 are formed in the through holes 50, 52, 54 by using a known film forming technique such as sputtering or CVD.
0 is formed. Finally, these individual electrodes 42, 44, 4
An insulating film 48 is formed on 6 and the resist film is removed.

FIG. 5 shows an ink jet head 1 of another embodiment.
0a is indicated. In the ink jet head 10a, a region of the third substrate 16 facing the diaphragm 30 includes:
A depression 70 having a constant depth is formed. Also,
Three individual electrodes 72, 74, 76 are stacked on the bottom of the recess 70, so that the distance from each individual electrode 72, 74, 76 to the diaphragm 30 is different. Further, an insulating film 78 is formed between the adjacent individual electrodes 72 and 74 and between the adjacent individual electrodes 74 and 76, and on the uppermost individual electrode 76, whereby a common electrode displaced between the adjacent individual electrodes and the diaphragm 30 is displaced. 32 and the individual electrodes 76 are prevented from contacting each other.

These depressions and individual electrodes are, for example, shown in FIG.
Is formed by the method shown in FIG. In this method, first, the substrate 16
Is etched on one side of the substrate. Next, CrAu is sputtered in the recess 70 to form an individual electrode 76 having a thickness of about 0.1 μm, and SiN is formed thereon by LP-CVD to form an insulating film 78. After that, the sputtering and the CVD are repeated to form the individual electrodes 74 and 72, and the insulating film 78 is formed between these and on the uppermost individual electrode 76. Note that the thickness of the uppermost insulating film 78 is preferably about 0.1 μm. These individual electrodes 7
2, 74 and 76 are connected to the switching circuit 62 via the conductive leads formed at the same time as the respective films are formed. Therefore, there is no need to form a through hole as in the above embodiment.

Incidentally, a voltage of 40 volts is applied to each individual electrode 7.
When applied to 2, 74, and 76, respectively, the ink ejection amounts in each case were 65 picoliters, 40 picoliters, and 25 picoliters.

It should be noted that the material of each member of the embodiment described above is not limited. For example, the electrode material includes
The material is not limited to CrAu, but may be any low-resistance material such as ITO, SnO ₂ , and Pt. The material of the insulating layer is not limited to SiN, but SiC, SiO ₂ , MgO or the like may be used.

Further, the arrangement of the plurality of individual electrodes is not limited to the above embodiment. For example, as shown in FIG. 7, a recess 80 having a bottom portion obliquely inclined is formed in the substrate 16 by etching. The three individual electrodes 82, 84, 86 may be arranged in this order along the inclination direction, or as shown in FIG.
0 may be formed by etching, and an individual electrode 92 may be arranged at the center and individual electrodes 94 and 96 may be arranged on both sides thereof.

Further, the number of individual electrodes is not limited to three, but may be two or more.

Further, although the common electrode 32 uses an ion doping layer, it may be formed by a known film forming technique such as sputtering similarly to the individual electrode. In addition, it is not necessary to provide each electrode independently, and when the substrate to which it is attached is formed of a conductive material, the substrate itself can be used also as an electrode.

In the above description, a plurality of individual electrodes are provided. However, a plurality of common electrodes may be provided, and a voltage may be selectively applied to the plurality of common electrodes through a switching circuit.

In the embodiment in which a plurality of electrodes are stacked, these electrodes are completely overlapped. However, at least a part of the electrodes may be overlapped. Also in this case, since the distance is different at the overlapping portion, the ink ejection amount can be changed by changing the electrode to which the voltage is applied, as in the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is an enlarged exploded perspective view of an inkjet head according to a first embodiment.

FIG. 2 is an enlarged sectional view of the ink jet head shown in FIG.

FIG. 3 is an enlarged partial plan view of a second substrate used in the inkjet head shown in FIG.

FIG. 4 is a process chart showing a method for forming an individual electrode.

FIG. 5 is an enlarged cross-sectional view of another embodiment of the inkjet head.

FIG. 6 is a process chart showing a method for forming the individual electrodes shown in FIG.

FIG. 7 is an enlarged sectional view showing another example of arrangement of individual electrodes.

FIG. 8 is an enlarged sectional view showing another example of arrangement of individual electrodes.

[Explanation of symbols]

10: inkjet head, 12: first substrate, 14
... 2nd substrate, 16 ... 3rd substrate, 20 ... ink, 22
... Ink chamber, 24 ... Nozzle, 30 ... Diaphragm, 32
... common electrodes, 36, 38, 40 ... individual electrodes.

Claims (4)

[Claims] A first electrode fixed on a substrate; a second electrode spaced from the first electrode; a diaphragm supporting the second electrode; A driving unit that applies a voltage between the first electrode and the second electrode, thereby deforming the diaphragm based on an electrostatic force generated between the first electrode and the second electrode; In the electrostatic ink jet head which pressurizes and discharges the ink housed in the vicinity of the diaphragm based on the deformation of the above, at least one of the first electrode and the second electrode is separated from each other by a plurality. An ink jet head comprising: a plurality of partial electrodes; and a distance between each of the first and second electrodes, which is the other electrode, and each of the partial electrodes is different. 2. The ink-jet apparatus according to claim 1, wherein the plurality of partial electrodes are arranged so as not to overlap each other when viewed from a direction in which the first electrode and the second electrode face each other. head. 3. The plurality of partial electrodes are arranged so as to at least partially overlap with other electrodes when viewed from the direction in which the first electrode and the second electrode face each other. The ink jet head according to claim 1, wherein 4. An insulating layer according to claim 3, wherein an insulating layer is interposed between the partial electrodes arranged so as to overlap when viewed from the facing direction of the first electrode and the second electrode. Ink jet head.