JPH11309849A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrostatic actuator type ink jet head for enhancing reliability by increasing a gap between electrodes and facilitating a manufacture. SOLUTION: This ink jet head 31 comprises a pair of diaphragms 55a, 55b formed of opposed walls in an ink channel 51, and electrodes 56, 72 of the side opposed to the channel 51 of the diaphragms 55a, 55b. an ink having higher relative permittivity than that of the air is filled between the electrodes 56 and 72 for generating an electrostatic force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic ink jet head which deforms a diaphragm by electrostatic force to discharge ink in an ink channel from a nozzle as a droplet.

[0002]

2. Description of the Related Art As a recording apparatus, there is an ink jet recording apparatus which forms an image by ejecting and flying ink droplets from nozzles and landing the ink droplets on a recording medium. There are various types of ink jet heads used in this recording apparatus. For example, an ink jet head using an electrostatic actuator that deforms a vibration plate by electrostatic force to discharge ink is known (for example, Japanese Patent Application Laid-Open No. H05-205605). 50601
Reference).

An electrostatic ink jet head generally has a laminated structure in which a channel plate provided with a plurality of recesses, and a glass substrate and a cover plate, which are disposed opposite to the bottom surface of the recesses, are joined. have. A nozzle for discharging ink droplets, an ink channel communicating with the nozzle, a diaphragm for changing the pressure in the ink channel, a common ink chamber for storing ink, and ink supply from the common ink chamber to the ink channel An inlet serving as a mouth is formed. The bottom wall of the ink channel is a diaphragm, and the ink channel generates pressure for discharging ink. A plurality of ink channels and nozzles are provided according to the number of dots to be printed. Further, a first electrode is provided on the back surface (the surface not facing the ink channel) of the vibration plate, and the second electrode is formed on the glass substrate at a position facing the first electrode with a small gap. It is provided on the upper surface. In order to form these electrode portions, concave portions are provided on the rear surface of the diaphragm and the upper surface of the substrate.

The principle of the ink discharging operation in the electrostatic ink jet head is as follows. When a voltage is applied from the drive circuit between the first and second electrodes, an electrostatic force is generated between the electrodes, and the diaphragm is attracted to the second electrode and bent.
At this time, since the volume of the ink channel increases, ink is supplied or filled into the ink channel from the common ink chamber through the inlet. Next, when the application of the voltage between the opposing electrodes is stopped and the electric charge is discharged, the diaphragm rapidly contracts the volume of the ink channel due to the restoring force due to its own rigidity, and ink is ejected from the nozzle by the pressure generated at this time. I do.

[0005] An ink jet head using such an electrostatic actuator can achieve a higher density and can perform printing at a relatively low voltage, as compared with a method in which ink is ejected by utilizing distortion of a piezoelectric element. There is an advantage that there is.

[0006]

However, in the case of an electrostatic ink jet head, it is necessary to make the gap between the first and second electrodes extremely small in order to suppress the applied voltage. is there. For example, the gap between the electrodes is set to about 0.3 μm. For this reason, when manufacturing a head, it is required to process or assemble individual parts such as a channel plate with extremely high precision.

Further, since the gap between the electrodes is very small, about 0.3 μm, the first electrode, which is an individual electrode, and the second electrode, which is a common electrode, come into contact with each other when driving the diaphragm to vibrate. Short circuit. It is conceivable to provide a protective layer on the electrode in order to prevent a short circuit, but there is a problem that the protective layer is easily affected by aging.

By the way, the pressure P generated by an ink-jet head using an electrostatic actuator is: P = ｛· {εrεo (V / d) ² } (1) where: εr: relative dielectric constant between opposed electrodes Rate εo: dielectric constant in vacuum (8.8 × 10 ⁻¹² [F /
m]) V: Applied voltage [V] d: Distance between electrodes [m]

In the case of the conventional electrostatic actuator, air (relative dielectric constant: 1) is contained in the gap between the electrodes. The gap must be 0.3 μm, and high precision processing and assembly are required. As is apparent from the above equation (1), it is understood that the pressure P generated by the electrostatic actuator increases as the relative permittivity εr between the opposing electrodes increases.

The present inventors have paid attention to the fact that the efficiency of an electrostatic actuator can be increased by interposing a substance having a relative permittivity larger than that of air between electrodes, and as a result, the gap between electrodes can be increased. As a result of diligent research, an inkjet head capable of improving the reliability and improving the reliability of the electrostatic actuator type inkjet head has been completed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrostatic actuator type ink jet head which can increase a gap between electrodes, facilitate manufacturing and enhance reliability.

[0012]

According to the first aspect of the present invention, there is provided a nozzle, an ink channel communicating with the nozzle, and a pressure control device for changing a pressure in the ink channel. A vibrating plate, wherein the vibrating plate is deformed by electrostatic force to discharge ink in the ink channel from the nozzle as droplets, and is formed by opposed walls of the ink channel. And a pair of vibration plates, and an electrode provided on the side of each of the vibration plates facing the ink channel, and ink is filled between the pair of electrodes that generate the electrostatic force. An ink jet head characterized in that:

The invention according to a second aspect is characterized in that ink is ejected when a voltage is applied between the pair of electrodes and the pair of diaphragms are attracted to each other.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a perspective view showing an ink jet printer 1 incorporating an electrostatic ink jet head according to Embodiment 1 of the present invention.

[0016] The ink jet printer 1 is provided with paper or OH.
It prints on a recording sheet 2, which is a recording medium such as a P sheet, and includes an inkjet head scanning system and a recording sheet feeding system.

The inkjet head scanning system includes a head unit 3 including a single or multiple colors (for example, three, four, or seven colors) of inkjet print heads.
A carriage 4 for holding the head unit 3, a scan shaft 5 and a guide shaft 6 for reciprocating the carriage 4 in parallel with the recording surface of the recording sheet 2, and reciprocatingly driving the carriage 4 along the guide shaft 6. A pulse motor 7; an idle pulley 8 for changing the rotation of the pulse motor 7 into a reciprocating motion of the carriage 4;
It is composed of

On the other hand, the recording sheet feeding system includes the recording sheet 2
, Which also serve as a guide plate for guiding the recording sheet 2 along the transport path, a paper pressing plate 11 for pressing the recording sheet 2 between the platen 10 to prevent floating, and a discharge roller 12 for discharging the recording sheet 2; A discharge holding roller 13;
The head unit 3 includes a maintenance device 14 for cleaning the nozzle surface of the head unit 3 that discharges ink and recovering a defective ink discharge from a good state, and a paper feed knob 15 for manually conveying the recording sheet 2.

The recording sheet 2 is fed to a recording section where the head unit 3 and the platen 10 face each other by a sheet feeding device such as a manual feed or a cut sheet feeder (not shown). At this time, the rotation amount of a paper feed roller (not shown) is controlled, and the conveyance to the recording unit is controlled. The paper feed roller is driven by a paper feed motor (not shown).

The print head of the head unit 3 includes:
An ink jet head 31, which will be described in detail later, is used, and ink droplets ejected from the ink jet head 31 land on the recording sheet 2 to form an image.

The carriage 4 is driven by a pulse motor 7, an idle pulley 8, and a timing belt 9.
Is scanned in the horizontal direction (main scanning), and the head unit 3 attached to the carriage 4 records an image for one line. Each time printing of one line is completed, the printing sheet 2 is fed in the vertical direction (sub-scan), and printing is performed on the next line.

The image is recorded on the recording sheet 2 in this manner, and the recording sheet 2 that has passed through the recording section is contacted with a discharge roller 12 disposed downstream of the recording sheet 2 at a constant pressure by a discharge press roller. 13 to be discharged.

FIG. 2 shows a carriage 4 including an ink jet head 31 for one color of the head unit 3 shown in FIG.
FIG. 3 is a perspective view for explaining a peripheral configuration.

In the vicinity of the carriage 4, an ink cartridge 403 containing ink and having a vent 404, a casing 401 containing the ink cartridge 403, a casing lid 405, and an ink cartridge 31 for detachably attaching the ink cartridge 403 to the ink jet head 31. Of the ink supply pipe 402 to be supplied to the casing 401, the hook 406 for fixing the casing lid 405 to the casing 401 when the casing lid 405 is closed, the lid stopper 407, and the direction for accommodating the ink cartridge 403 (the direction of arrow D3). A pressing spring 408 is provided to hold the ink cartridge 403 in the casing 401 between the casing lid 405 and the ink cartridge 403 while urging the ink cartridge 403 in the opposite direction.

When the carriage 4 having such a configuration moves in the scanning direction (the direction of the arrow D1), the recording sheet 2 is main-scanned. Also, recording sheet 2
Is sent in the sub-scanning direction (the direction of arrow D2).
Will be printed.

FIG. 3 is a sectional view showing the structure of the ink-jet head, FIG. 4 is a perspective view showing a channel plate of the ink-jet head, FIGS. 5 (A) and 5 (B) are lines AA in FIG. It is sectional drawing which follows the BB line.

The ink jet head 31 of the first embodiment shown in FIG. 3 is an edge eject type head for discharging ink droplets from a nozzle 54 provided at the head side end (the left end in the figure). As shown in FIG. 2, two channel plates 50a and 50b made of single crystal silicon and provided with a plurality of concave portions are vertically stacked in the figure.

The concave portions provided on the inner surface side of each of the channel plates 50a and 50b face each other, so that the ink jet head 31 has a plurality of nozzles 54 for discharging ink, and the ink communicates with the respective nozzles 54 to allow the ink to pass therethrough. A plurality of ink channels 51 for generating pressure for ejection, one common ink chamber 52 for storing ink supplied from a tank (not shown), and ink supply ports from the common ink chamber 52 to each ink channel 51 Is formed. For example, the ink channel 51 includes a concave portion 51a provided on the channel plate 50a shown on the upper side in FIG. 4 and a concave portion 51b provided on the channel plate 50b shown on the lower side.
Are formed by facing each other. In addition,
Reference numeral “58” in the figure indicates an ink supply hole for supplying ink to the common ink chamber 52.

A pair of diaphragms 55a, 55a,
55b is formed, and the diaphragms 55a and 55b are slightly displaced, so that the volume or the internal pressure of the ink channel 51 can be changed.

In particular, in the first embodiment, as shown in FIGS. 3 and 5A, a first electrode 56 is provided on the inner surface (the surface facing the ink channel 51) of the diaphragm 55a. As shown in FIGS. 3 and 5B, the diaphragm 55b
Is provided with a second electrode 72 on its inner surface. Referring to FIG. 3, first electrode 56 is a common electrode, and second electrode 72 is an individual electrode or a drive electrode.
Connected to the drive circuit 110.

The driving circuit 11 is provided between the pair of electrodes 56 and 72.
By applying a predetermined voltage from 0, the pair of diaphragms 55a and 55b are attracted to each other to
1 is contracted sharply, and the ink droplets are ejected from the nozzles 54 by the pressure generated at this time. On the other hand, when the application of the voltage between the electrodes is stopped and the electric charge is discharged, the diaphragms 55a and 55b increase the volume of the ink channel 51 by the restoring force due to their rigidity, and the common ink chamber 52
The ink is supplied or filled into the ink channel 51 from the inlet 53 through the inlet 53.

The first electrode 56 as the common electrode and the second electrode 72 as the individual electrode face the inside of the ink channel 51 so as to form a part of the ink flow path. In other words, the ink channel 5 is provided between the common electrode and the individual electrode.
1 is provided. Therefore, the space between the pair of electrodes 56 and 72 that generate the electrostatic force does not contain air, and is filled with ink.

In the case of an aqueous ink, the relative dielectric constant εr is about 6
0, air (relative permittivity 1) between the electrodes 56 and 72
A substance having a higher relative dielectric constant than the above is interposed. Therefore, the efficiency of the electrostatic actuator is increased, and the gap d between the electrodes can be made very large. While the gap between the electrodes of the conventional head was about 0.3 μm, in the first embodiment, the gap d between the electrodes of about 3 μm, which is about 10 times, was increased.
Has taken.

Next, a method of manufacturing the ink jet head 31 will be briefly described. The inkjet head 31 according to the first embodiment is manufactured using a so-called semiconductor device manufacturing process, a micro-machine manufacturing process, or the like, and various methods are available.
An example will be described. It is needless to say that the present invention can be applied to an inkjet head manufactured by a method other than the manufacturing method described here.

FIGS. 6A to 6H are schematic process diagrams for explaining a method of manufacturing an ink jet head.

First, as shown in FIG. 6 (A), in order to form holes for taking out electrodes, the substrate 100 made of single crystal silicon before etching is provided with a number corresponding to the number of ink channels 51. A through hole 101 is opened from the back side (upper side in the figure) by sandblasting. Further, a through-hole 102 for forming the ink supply hole 58 is similarly opened. At this time, the through holes 101 and 102
Slightly tapered.

Ink channel 51, common ink chamber 5
2, inlet 53, nozzle 54 and diaphragm 55a,
Channel plates 50a, 5b for forming 55b
The recess provided in Ob is formed by anisotropic etching using a KOH aqueous solution. The silicon substrate 100 has a thickness of 2
The orifice flat is set to (1,1,0) with a plane orientation (1,1,0) of 00 μm. Then, a resist 103 is formed on the back surface and the front surface (the lower surface in the figure) of the substrate 100, and a channel pattern is arranged at an angle of 35.3 ° from the orifice flat and etched to form a predetermined standing wall structure ( FIG. (B).

After the resist 103 is removed (FIG. 4C), the portion of the silicon substrate indicated by the arrow is cut by a dicer to form an ink discharge port (nozzle 54) (FIG. 4D).

Next, the tapered through hole 1
01 Cr on the inner surface from the back side by sputtering, CVD, etc.
An Au film is formed, and a CrAu film is formed to a thickness of 0.1 μm from the surface side by sputtering, CVD, or the like to form an electrode 56 (FIG. 10E). In addition, as a material for forming the electrode,
In addition to CrAu, any low-resistance material such as ITO, SnO2, and Pt can be used.

Further, as a protective layer 104 on the electrode,
iC is sputtered by 0.1 μm (FIG. (F)).
As the protective layer, SiO2 and MgO can be used in addition to SiC, but SiC is most preferable in consideration of moisture resistance.

According to the same procedure as described above, a channel plate 50b symmetrical to the channel plate 50a is also manufactured.

Then, the channel plates 50a, 50
The low-melting glass 105 is simulated on the joint surface b (FIG. 9G), and the channel plates 50a and 50b are joined to complete the ink jet head 31. The thickness of the diaphragms 55a and 55b is 3 μm, and the gap d between the electrodes is 3 μm.

The ink jet head 31 of the first embodiment
Has a configuration in which ink having a higher dielectric constant than air is filled between the electrodes 56 and 72, so that the efficiency of the electrostatic actuator can be increased, and the gap d between the electrodes can be made much larger than that of the conventional head. it can. As a result, processing and assembling of the channel plates 50a and 50b, which are components of the inkjet head 31, are greatly facilitated,
The head can be easily manufactured, and the yield can be improved.

The electrodes 56 and 72 of the ink jet head 31 manufactured as described above are connected to an electrostatic actuator driving circuit. FIG. 7 is a schematic block diagram showing the driving circuit 110.

The driving circuit 110 includes a charging circuit 112 connected to the power supply circuit 111 and a discharging circuit 113 connected to the ground.
A switch circuit 114 for selectively connecting an electrostatic actuator having a pair of electrodes 56 and 72 to the charging circuit 112 or the discharging circuit 113; and a clock circuit 115 for outputting a clock pulse as a reference for operation timing.
And a timer circuit 1 for taking charge or discharge timing
16. When ejecting ink, it is necessary to perform an operation of drawing the pair of diaphragms 55a and 55b to each other steeply. The drive circuit 110 is provided with the diaphragm 55
A voltage pulse for realizing the operations of a and 55b is generated, and application and cutoff of the drive voltage to the electrodes 56 and 72 are controlled.

When a drive voltage of 35 V was applied to the ink jet head 31 of the first embodiment, about 60 picoliters (pl) of ink droplets were ejected. In a conventional inkjet head having one diaphragm, a driving voltage of 40 V was applied to eject the same amount of ink droplets.
The voltage can be reduced as compared with the conventional head. this is,
In this inkjet head 31, two diaphragms 55
This is because the ink channel 51 is sandwiched between a and 55b, so that a large desired displacement volume can be easily obtained as compared with the conventional example in which one diaphragm is used.

Furthermore, the conventional type (interelectrode gap 0.3 μm)
m) was short-circuited by 500 million times driving, whereas the head 31 of the first embodiment (inter-electrode gap d = 3 μm) can have a larger inter-electrode distance than the conventional type, so that the electrodes 56 and 72 There was no contact between them, no short circuit was observed even after driving 2 billion times, and it was found that they were hardly affected by aging. As described above, a highly reliable head 31 can be manufactured in terms of durability.

Embodiment 2 FIG. 8 is a sectional view showing the structure of an ink jet head according to Embodiment 2, and FIG. 9 is an exploded perspective view showing the same ink jet head.

In the second embodiment, two diaphragms 155
a, 155b is arranged at a position slightly apart from the substantial ink flow path from the inlet 153 to the nozzle 154, and the space between the two diaphragms 55a, 55b forms a part of the ink flow path. This is different from the first mode.

The ink jet head 131 of the second embodiment
Is constituted by superposing two channel plates 150a and 150b made of single crystal silicon provided with a plurality of concave portions on the upper and lower sides in the figure and joining a nozzle plate 160 having a nozzle 154 formed at a side end thereof. I have.

A part of the ink channel 151 extends rearward (to the right in FIG. 8) with respect to the nozzle 154,
The upper and lower walls of the extension 161 are connected to the diaphragm 155a,
155b. A first electrode 156 serving as a common electrode is provided on the inner surface of the diaphragm 155a.
A second electrode 172 serving as an individual electrode is provided on the inner surface of b. The inlet 153 is provided for the channel plate 150a.
And ink is supplied from an ink chamber (not shown).

Both nozzle diameter and inlet diameter are 23 μm
It is. The nozzle plate 160 is manufactured by Ni electroforming. In addition, etching from both sides of the silicon substrate, two-step etching, how to open through holes, a method of forming electrodes,
The method of joining the substrates and the like are the same as in the first embodiment. Further, the same materials as those of the first embodiment can be used for the materials of the electrodes and the protective layer.

The discharge operation is the same as in the first embodiment.
By applying a predetermined voltage from the drive circuit 110 between 56 and 172, the diaphragms 155a and 155b are attracted to each other to rapidly contract the volume of the ink channel 151, and the ink droplets are ejected by the pressure generated at this time. Fifteen
4 is discharged. On the other hand, when the application of the voltage between the electrodes 156 and 172 is stopped to discharge the electric charge, the diaphragm 155
a and 155b increase the volume of the ink channel 151 by the restoring force due to its own rigidity,
Is supplied to the ink channel 151 through the ink channel 151.

The ink jet head 131 having such a configuration
However, since the ink having a higher dielectric constant than the air (relative dielectric constant: about 60) is filled between the electrodes 156 and 172, the gap d between the electrodes is much larger than that of the related art, for example, 3 μm. As a result, the manufacture of the electrostatic actuator type inkjet head is facilitated and the reliability is enhanced.

Moreover, the two diaphragms 155a, 155b
Is arranged at a position rearward of the inlet 153 with respect to the nozzle 154 and is slightly separated from the substantial ink flow path, so that the flow of ink in the ink flow path from the inlet 153 to the nozzle 154 may be obstructed. Absent. Thereby, the ink jet head 3 of the first embodiment
Compared with No. 1, high-speed printing performance can be improved.

In Embodiments 1 and 2, the channel plate is formed by wet etching of a silicon substrate, but may be formed by dry etching with HF. In this case, the etching surface is not affected by the plane orientation, and a channel pattern similar to that of the mask can be manufactured. In addition, other than silicon, photosensitive glass, polyimide or polysulfone which is a resin excellent in ink resistance (made by molding or the like) can be used instead.

Although the case where the protective layer is formed on the electrode in order to prevent a short circuit via the ink has been described, it is necessary to form the protective layer when using an insulating ink. There is no.

As shown in FIG. 10, the present invention can be applied to a face eject type head 231.
The head 231 has two channel plates 250
a, 250b are vertically overlapped in the figure, and a nozzle 254 is formed on the lower surface of the channel plate 250b. Note that members common to those shown in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted.

[0059]

As described above, according to the present invention, it is possible to provide an electrostatic actuator type ink jet head in which the gap between the electrodes can be made large, the production is facilitated and the reliability is improved. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an inkjet printer incorporating an electrostatic inkjet head according to a first embodiment of the present invention.

FIG. 2 is a perspective view for explaining a configuration around a carriage 4 including an inkjet head for one color of the head unit shown in FIG.

FIG. 3 is a cross-sectional view illustrating a structure of an inkjet head.

FIG. 4 is an exploded perspective view showing a channel plate of the inkjet head.

5 (A) and 5 (B) are AA of FIG. 3, respectively.
It is sectional drawing which follows a line and a BB line.

FIGS. 6A to 6H are schematic process diagrams for explaining a method of manufacturing an ink jet head.

FIG. 7 is a schematic block diagram illustrating a drive circuit.

FIG. 8 is a cross-sectional view illustrating a structure of an inkjet head according to a second embodiment.

FIG. 9 is an exploded perspective view showing the inkjet head.

FIG. 10 is a cross-sectional view illustrating a structure of a face-ejection type inkjet head.

[Explanation of symbols]

31, 131, 132 ... inkjet heads 50a, 50b, 150a, 150b, 250a, 25
0b channel plate 51, 151 ink channel 54, 154, 254 nozzle 55a, 55b, 155a, 155b diaphragm 56, 156 first electrode 72.172 second electrode 110 drive circuit d gap between electrodes

Claims (2)

[Claims] A nozzle, an ink channel communicating with the nozzle, and a vibrating plate for changing a pressure in the ink channel, wherein the vibrating plate is deformed by an electrostatic force to form an ink in the ink channel. And a pair of diaphragms formed by opposed walls of the ink channel, and an electrode provided on a side of each of the diaphragms facing the ink channel. An ink jet head comprising: a space between a pair of electrodes that generate the electrostatic force; 2. The ink jet head according to claim 1, wherein a voltage is applied between said pair of electrodes to eject ink when said pair of diaphragms are attracted to each other.