JPH11291484A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head which can be driven with a low voltage through a relatively wide gap. SOLUTION: The ink jet head comprises a nozzle 22, an ink channel 18 communicating with the nozzle, a diaphragm 19 provided at a part of the ink channel 18, a common electrode 34 arranged on the diaphragm 19, and a drive electrode 38 disposed oppositely to the common electrode 34 wherein a pulse voltage is applied between the common electrode 34 and the drive electrode 38 to deform the diaphragm 19 with electrostatic force thus ejecting an ink drop for printing from the nozzle 22 toward a recording paper. A resilient dielectric member is provided between the common electrode 34 and the drive electrode 38.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as an inkjet head of an electrostatic actuator type, for example, Japanese Patent Laid-Open No. 6-340069 is used.
8 or JP-A-7-246706 discloses an ink jet head 100 shown in FIG. The inkjet head 100 is configured by integrally joining a cover plate 12, a channel plate 14, and a substrate 16 together.

The channel plate 14 is made of a silicon plate, and has a plurality of grooves formed by anisotropic etching. These grooves correspond to the cover plate 12.
The ink channel 18 that accommodates the ink, the nozzle 22 that ejects the ink in the ink channel 18 as droplets, and the common ink chamber 2 that accommodates the ink supplied to the ink channel 18 are covered by the ink channel 18.
6 and an inlet 30 for communicating the ink channel 18 with the common ink chamber 26.

The bottom of the ink channel 18 is provided with a diaphragm 19
The ink channel 18 of the diaphragm 19
A common electrode 34 is formed on the surface on the opposite side. On the other hand, a concave portion 36 is formed at a position corresponding to the ink channel 18 on the substrate 16, and a drive electrode 38 is formed on the bottom surface of the concave portion 36 so as to face the common electrode 34.

In the ink jet head 100 having the above-described structure, when voltages of different polarities are applied to the common electrode 34 and the driving electrode 38, respectively, the two electrodes 34,
The diaphragm 19 bends and deforms toward the drive electrode 38 due to the attraction of 38. This deformation increases the volume in the ink channel 18, and accordingly, ink is drawn from the common ink chamber 26 into the ink channel 18 via the inlet 30. When the voltage application to the electrodes 34 and 38 is released, the diaphragm 19 returns to its original state due to its own elasticity. At this time, the ink in the ink channel 18 is pressurized, and the ink droplet 46 is ejected from the nozzle 22.

[0006]

However, in the above-described ink jet head 100, if the driving is to be performed at a relatively low voltage, the gap between the common electrode 34 and the driving electrode 38 needs to be formed very small, for example, 0.3 μm. Therefore, extremely high precision is required for processing and assembly. On the other hand, if the gap is increased to facilitate processing and assembly, the driving must be performed at a high voltage of, for example, 200 to 300 volts, and there is a problem that the driving circuit becomes very expensive.

Accordingly, an object of the present invention is to provide an ink jet head which can be driven at a low voltage with a relatively wide gap between electrodes in order to solve the above problems.

[0008]

In order to achieve the above object, the present invention provides a nozzle, an ink flow path communicating with the nozzle, a diaphragm provided in a part of the ink flow path, and a diaphragm. And a counter electrode provided opposite to the diaphragm electrode, a pulse voltage is applied between the diaphragm electrode and the counter electrode, and the diaphragm is subjected to electrostatic force. In the ink jet head for performing printing by discharging the ink droplets from the nozzles toward the recording paper by this deformation and performing printing, an elastic dielectric member is provided between the diaphragm electrode and the counter electrode. Is what you do.

In this ink jet head, the dielectric member may include a void or a bubble.

[0010]

According to the ink jet head of the present invention, by providing a dielectric member between the diaphragm electrode and the opposing electrode, the electric field strength can be increased even in the same gap between the electrodes, thereby increasing the electrostatic force. it can. Therefore, when trying to obtain the same amount of deformation for the diaphragm, the gap between the electrodes can be made wider than before, and low-voltage driving becomes possible. Further, the dielectric member prevents an electrical short circuit between the diaphragm electrode and the counter electrode due to its insulating property. Further, since the dielectric member has elasticity, the diaphragm can be deformed even if a dielectric member is provided between the electrodes, and the diaphragm electrode or the counter electrode is damaged by absorbing the shock at the time of the deformation of the diaphragm. Can be prevented.

In the ink jet head in which the dielectric member contains voids or bubbles, the dielectric member is more easily deformed, so that a large amount of deformation of the diaphragm can be obtained and further low voltage driving is possible. become.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a plan view of an inkjet head 10 according to the present invention, FIG. 2 is a sectional view taken along line AA in FIG. 1, and FIG. 3 is a sectional view taken along line BB in FIG. In the inkjet head 10, the cover plate 12, the channel plate 14, and the substrate 16 are laminated and integrally joined by anodic joining.

The cover plate 12 is, for example, a flat plate made of glass and covers an upper portion of the channel plate 14. The channel plate 14 is made of, for example, a silicon plate, and has a plurality of grooves formed on its upper surface by anisotropic etching. Specifically, a plurality of long grooves 20 to be ink channels (ink flow paths) 18 are arranged in parallel with each other. In addition, the channel plate 14
The narrow groove 24 which becomes the nozzle 22 is provided at the edge of the long groove 2.
0 is formed. Further, on the opposite side of the narrow groove 24 of the channel plate 14, the common ink chamber 2 is provided.
The lateral grooves 28 which are 6 extend in the arrangement direction of the plurality of long grooves 20. The long groove 20 serving as the ink channel 18 and the lateral groove 28 serving as the common ink chamber 26
They communicate with each other through narrow grooves 32 that serve as inlets 30. By covering these grooves 20, 24, 28, 32 with the cover plate 12, the ink channel 18, the nozzle 22, the common ink chamber 26, and the inlet 30 are respectively formed.

The nozzle 22 communicates with the ink channel 18 and discharges the ink in the ink channel 18. Further, the ink channel 18 and the common ink chamber 26 communicate with each other via an inlet 30, and ink is supplied from the common ink chamber 26 to each of the ink channels 18 to be stored therein. Further, the common ink chamber 26 is connected to an ink tank (not shown) via an ink supply path 29, from which ink is supplied.

A plurality of rectangular recesses 15 are formed at positions corresponding to the respective ink channels 18 on the surface of the channel plate 14 facing the substrate. A common electrode (diaphragm electrode) 34 is formed on the diaphragm 19 which is the ceiling of the recess 15 and the bottom of the ink channel 18 by sputtering a metal material on the surface on the side of the recess 15. I have. On the other hand, a substrate 1 made of, for example, glass
A plurality of drive electrodes (counter electrodes) 38 are formed on the surface of the common electrode 3 by sputtering a metal material on the surface of the common electrode 3.
4 are formed opposite to each other. The common electrode 34 and the drive electrode 38 are electrically connected to a drive circuit 40, respectively.

Between the common electrode 34 and the drive electrode 38,
The dielectric member 42 having elasticity is filled. In the present embodiment, the dielectric member 42 is formed of, for example, silicone rubber. As shown in FIG. 3, the dielectric member 42 and the recess 1
It is preferable to leave a space between the side walls 5. The reason is that if there is a space that expands to the side when the deformation of the diaphragm 19 is compressed, the dielectric member 42 is also easily bent and deformed with the deformation of the diaphragm 19. However, since the dielectric member 42 itself has elasticity, the diaphragm 19 can be deformed without this space. Therefore, the space between the dielectric member 42 and the side wall of the recess 15 is not an essential requirement of the present invention.

Next, the ink discharging operation of the ink jet head 10 having the above configuration will be described. The ink supplied from the ink tank (not shown) to the common ink chamber 26 via the ink supply path 29 is supplied to the corresponding inlet 3.
Each of the ink channels 18 is accommodated in each of the ink channels 18. In this state, when a pulse voltage is applied from the drive circuit 40 to the drive electrode 38, the common electrode 34 to which a voltage having a polarity different from the pulse voltage is applied is attracted by electrostatic force, and the diaphragm 19 is deformed. This deformation increases the volume of the ink channel 18, and accordingly, ink is drawn into the ink channel 18 from the common ink chamber 26 via the inlet 30. When the voltage application to the drive electrode 38 is instantaneously released, the diaphragm 19
Returns to its pre-deformation state due to its own elastic restoring force. At this time, the volume of the ink channel 18 is rapidly reduced, the internal ink is pressurized, and the ink droplets are ejected from the nozzles 22. The ink droplets adhere to a recording medium such as a sheet of paper (not shown) to form dots, and an image is recorded by a group of the dots.

Here, in order to eject ink normally,
Both the “displacement volume of the diaphragm” and the “restoring pressure of the diaphragm” need to satisfy predetermined values. The “displacement volume” is an item to be set according to the volume of the ink droplet to be ejected. On the other hand, the “restoration pressure” must be set to a pressure higher than the pressure required to accelerate the ink to a dischargeable level. The value of the restoration pressure is, for example, about 0.3 MPa when printing is performed with a dot diameter of several tens μm using the most common water-based ink at present. This pressure P is expressed by the following equation regardless of the material and thickness of the diaphragm.

[0019]

P = (1/2) ε _r ε ₀ [(V / (d−δ)] ² ... P: pressure ε _r : relative permittivity between gaps ε ₀ : vacuum permittivity (8.854) × 10 ⁻¹² F / m) V: Voltage d: Gap between electrodes δ: Deformation amount of diaphragm

When the gap between the electrodes is a gap as in the conventional ink jet head 100, the dielectric constant between the gaps is substantially equal to the dielectric constant of vacuum. Therefore, in order to make the pressure P 0.3 MPa or more in the above equation, the electric field strength [V / (d−δ)] ≧ 260 V / μm needs to be satisfied. Assuming that the driving voltage is 50 V, in order to obtain the electric field strength under the above conditions, the inter-electrode gap (d−δ) after the deformation is required.
Must be 0.2 μm or less, which requires extremely difficult high-precision processing and assembly.

On the other hand, in the ink jet head 10 of the present embodiment in which the dielectric member 42 made of silicone rubber is filled between the electrodes 34 and 38, the relative permittivity ε _{r of} silicone rubber is 8.5. Similar 0.3M
Electric field strength [V / (d−
δ)] is determined to be 90 V / μm from the above equation.
Therefore, when the inter-electrode gap (d−δ) after the deformation is set to 0.2 μm in the same manner as described above, the driving voltage is 18 V. Further, the gap (d−δ) between the electrodes after the deformation is set to 0.4.
If it is set to μm, the driving voltage may be 36 V.

As described above, in the ink jet head 10 according to the present embodiment, the electrostatic force can be enhanced by providing the dielectric member 42 between the electrodes 34 and 38.
Low voltage driving is possible with a relatively wide gap between electrodes.
Further, since the dielectric member 42 made of silicone rubber has an insulating property, it is possible to prevent an electrical short circuit from occurring between the common electrode 34 and the drive electrode. Further, the dielectric member 42
Has elasticity, the diaphragm 19 can be deformed even if the dielectric member 42 is filled between the electrodes, and the common electrode 34 and the drive electrode 38 are damaged by absorbing the shock when the diaphragm 19 is deformed. Can be prevented.

Next, an ink jet head 50 according to a second embodiment will be described with reference to FIG. In this inkjet head 50, the dielectric member 4 made of silicone rubber is used.
2a is divided into a plurality by slits 52 and includes a gap. Other configurations are the same as those of the inkjet head 10 of the first embodiment.

Here, when the dielectric member 42 made of silicone rubber is filled without gaps between the electrodes 34 and 38,
Is determined by the bulk modulus of the silicone rubber. The silicone rubber has a bulk modulus of about 50 MPa, whereas the electrostatic attraction force required to print a dot having a diameter of several tens of μm with a general water-based ink is 0.3 MPa, as described above. The compression ratio of rubber, that is, the displacement ratio of the diaphragm 19 to the gap between the electrodes is only about 1% at most.

On the other hand, in order to increase the displacement ratio of the diaphragm 19, as in the case of the ink jet head 50, the slit 5 is formed so that the dielectric member 42a is easily bent.
It is effective to form voids 2 to form voids. In this case, since the dielectric member 42a has a higher dielectric constant than the gap, the electric flux lines concentrate on the dielectric member. Therefore, the effective elastic modulus can be reduced without substantially reducing the effective dielectric constant. If the silicone rubber dielectric member 42a is expanded in the lateral direction by compression, its effective elastic modulus becomes equal to the Young's modulus. Since the Young's modulus of the silicone rubber is about 1.5 to 5 MPa, the diaphragm 1
It can be seen that No. 9 can be displaced up to about 10% with respect to the gap between the electrodes.

As described above, according to the ink jet head 50 of the second embodiment, the provision of the gap 52 makes it easier for the dielectric member 42a to be deformed.
9 can be further increased, and further lower voltage driving is possible.

Next, an ink jet head 60 according to a third embodiment will be described with reference to FIGS. In the ink jet head 60, a large number of air bubbles 62 are included in the dielectric member 42b made of silicone rubber to facilitate deformation. As a method for manufacturing such a dielectric member 42b, a method in which an elastic resin in which bubbles are uniformly dispersed is poured in a liquid phase and then cooled and solidified, or an elastic film containing bubbles in advance is applied to the electrodes 34 and 38 For example, a method of sandwiching it between them is considered. The configuration other than the dielectric member 42b is the same as the inkjet head 1 of the first embodiment.
Same as 0.

According to the ink jet head 60,
Microscopically, as shown by the dotted line in FIG.
When pressure is applied to 2b, the dielectric member 42b is deformed so that the internal bubbles are crushed. Therefore, when viewed macroscopically, the dielectric member 42b is much softer than its own elastic modulus. Therefore, as in the second embodiment, the amount of deformation of the diaphragm 19 can be further increased, and the dielectric member 42b can be further reduced. Voltage drive becomes possible.

The appropriate value of the bubble rate in the dielectric member 42b was considered by a simple method. FIG. 8 is a graph showing the relationship between the pressure and the compression deformation rate when two types of resin films having a bubble rate are pressed. From this graph, in each case, the compression deformation rate increases almost linearly with the increase in applied pressure until the compression deformation rate becomes about one third of the bubble rate, but gradually increases as the compression deformation rate further increases. It can be seen that the rate of increase has slowed. Further, when the displacement volume of the diaphragm 19 is equal to or larger than the total bubble volume, all the bubbles are almost completely crushed, so that the effect of including the bubbles is almost eliminated. Therefore, the dielectric member 4
If the total volume of the bubbles provided in 2b is between 1 and 3 times the displacement volume of the diaphragm 19, it can be seen that the dielectric member 42b can be effectively deformed according to the deformation of the diaphragm 19.

In each of the embodiments described above, silicone rubber is used as the material of the dielectric member. However, the present invention is not limited to this. Any material having low rigidity and high dielectric constant can be used. For example, a rubber-based material such as neoprene rubber or urethane rubber, or a resin having a relatively low elastic modulus such as polyethylene or polybutylene can be used. Since the relative permittivity of these materials is about 2 or more, the driving voltage can be reduced by about 30% or more when calculated from the above equation. Also, for example, a high dielectric substance (for example, B
When a powder in which a powder of aTiO ₃ (relative permittivity ε _r ≒ 5000) is dispersed is used, the effective relative permittivity can be 1000 or more.

In the present invention, it is sufficient that a substance having a high dielectric constant is filled so as to be easily deformed between the electrodes and to increase the effective electric field strength, and the material and structure to be filled are not particularly limited. Absent. For example, the object of the present invention is achieved even with the following. -Fill the elastic resin beads. -Enclose a liquid including gas. -Fill a sol or gel dielectric. -The fluid filler and the elastic material are mixed and filled. Mixing and filling a fluid filler and flexible microcapsules containing gas inside.

In each embodiment of the present invention described above,
Although the common electrode 34 is provided on the diaphragm 19 side, a drive electrode may be provided on the diaphragm 19 side and a common electrode may be provided on the substrate 16 side. In the above embodiments, the diaphragm 19 is provided with an electrode made of a metal thin film by sputtering. However, the diaphragm made of silicon is provided with conductivity by performing boron doping so that the diaphragm itself becomes a common electrode or a driving electrode. The present invention is also applicable when used as

[Brief description of the drawings]

FIG. 1 is a plan view of an inkjet head according to a first embodiment.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a sectional view taken along line BB in FIG. 2;

FIG. 4 is a partial cross-sectional view of an inkjet head according to a second embodiment.

FIG. 5 is a partial cross-sectional view of an inkjet head according to a third embodiment.

6 is a partially enlarged view of the dielectric member shown in FIG.

7 is a graph showing a result of examining a relationship between an applied pressure and a compressive deformation ratio of the dielectric member shown in FIG. 6;

FIG. 8 is a partial cross-sectional view illustrating an example of a conventional inkjet head.

[Explanation of symbols]

18 ink channel (ink flow path), 19 diaphragm, 22 nozzle, 34 common electrode (diaphragm electrode), 3
8 ... drive electrode (counter electrode), 42, 42a, 42b ... dielectric member.

Claims (2)

[Claims] A nozzle, an ink flow path communicating with the nozzle, a vibrating plate provided in a part of the ink flow path, a vibrating plate electrode provided on the vibrating plate, and a vibrating plate electrode. A pulse voltage is applied between the diaphragm electrode and the counter electrode, the diaphragm is deformed by electrostatic force, and the deformation causes ink droplets to be discharged from the nozzles on the recording paper. An ink jet head which performs printing by discharging toward an ink jet head, wherein an elastic dielectric member is provided between the diaphragm electrode and the counter electrode. 2. The ink jet head according to claim 1, wherein said dielectric member includes a void or a bubble.