JP2008087438A - Liquid injection jet head and liquid injection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid injection head and a liquid injection apparatus wherein durability under an continuous operation is improved by stabilizing a liquid injection characteristic, and a gradation expression is widened. <P>SOLUTION: The liquid injection head comprises a plurality of pressure chambers 11 communicating with nozzles 21 which inject droplets, each having: a flexible electrode 15 arranged on one surface of the pressure chamber; and a fixed electrode 33 opposed to the flexible electrode 15 at a constant interval. A drive voltage pulse is applied between the flexible electrode 15 and the fixed electrode 33, and the flexible electrode 15 is vibrated by the electrostatic force produced between them, so that the nozzle 21 is made to discharge droplets from the nozzle 21 by producing a pressure change in the pressure chamber 11. An 113-138 mm thick insulation film consisting of an oxide film, is provided in a region of the flexible electrode 15 opposed to the fixed electrode 33. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid ejecting head and a liquid ejecting apparatus that eject liquid from a nozzle opening by electrostatic force, and relates to an ink jet recording head and an ink jet recording apparatus that eject ink as liquid.

  Generally, various types of liquid ejecting heads such as ink jet recording heads used in printers, facsimiles, copiers, and the like are known depending on the mechanism for ejecting droplets. For example, the liquid is boiled by a heating element, etc., and droplets are ejected by the bubble pressure generated at that time, or the volume of the pressure generation chamber filled with the droplets is expanded or contracted by the displacement of the piezoelectric element. There are those that discharge droplets from a nozzle. Further, for example, there is one in which droplets are ejected from a nozzle by changing the volume of a pressure generating chamber using electrostatic force.

  For example, as an electrostatic drive type ink jet recording head, a nozzle plate having a plurality of nozzles, a liquid chamber (pressure chamber) communicating with the nozzles, and a flexible electrode defining one surface of the liquid chamber There is a structure in which a first substrate provided with an electrode substrate and an electrode substrate provided with individual electrodes arranged to face a flexible electrode at regular intervals are attached (for example, see Patent Document 1).

  Moreover, in patent document 1, an insulating film is provided in the area | region which opposes the fixed electrode of a flexible electrode, The short circuit of the circuit when a flexible electrode bends and deform | transforms by this insulating film and contact | abuts to a fixed electrode. In addition, sticking of the flexible electrode to the fixed electrode is prevented.

JP 2004-284098 A (7th page, FIGS. 1 to 3)

  When the insulating film formed on such a flexible electrode is thick, the electric field strength between the flexible electrode and the fixed electrode is weakened, and the rigidity of the flexible electrode is increased. The flexible electrode cannot be subjected to desired bending deformation, and desired ink ejection characteristics cannot be obtained. For this reason, it is formed with a minimum film thickness (for example, a film thickness of about 100 nm) in consideration of a withstand voltage that can withstand a voltage applied between the flexible electrode and the fixed electrode.

  However, if the flexible electrode is repeatedly bent and deformed, and the insulating film on the flexible electrode and the fixed electrode are repeatedly contacted and peeled off, charges are accumulated and charged in the insulating film, and the vibration plate There is a problem that the initial stable position is deviated, the electric field at the time of energization is affected, the behavior of the flexible electrode is deviated, and stable ink ejection characteristics cannot be obtained.

  Further, there is a problem that the insulating film is attached to the fixed electrode in a state where the flexible electrode is bent and deformed due to charging.

  Furthermore, examples of the drive voltage pulse for ejecting ink include one that ejects ink droplets 1 to 3 times within a predetermined time to print one dot. Among these, when 1-dot printing is performed by ejecting ink droplets two or three times, the voltage applied between the flexible electrode and the fixed electrode must be continuously applied so that the polarity is reversed. Thus, charging of the insulating film can be prevented. However, when ink droplets are ejected once to perform printing of one dot, the same polarity voltage is continuously applied to the flexible electrode and the fixed electrode, and the insulating film Since charging is performed, ink droplets cannot be ejected once to perform printing of one dot, and there is a problem that gradation expression at the time of printing is limited.

  Such a problem exists not only in an ink jet recording head that ejects ink droplets but also in a liquid ejecting head that ejects liquid other than ink.

  In view of such circumstances, the present invention provides a liquid ejecting head and a liquid ejecting apparatus that can stabilize liquid ejecting characteristics, improve durability by continuous driving, and widen gradation expression. Is an issue.

According to a first aspect of the present invention for solving the above-described problem, a plurality of pressure chambers communicating with a nozzle from which droplets are ejected, a flexible electrode provided on one surface of the pressure chamber, and the flexibility A fixed electrode disposed opposite to the electrode at a predetermined interval, and a driving voltage pulse is applied between the flexible electrode and the fixed electrode, and the flexible electrode is generated by an electrostatic force generated therebetween. Is a liquid jet head that generates a pressure fluctuation in the pressure chamber by vibrating the nozzle and ejects droplets from the nozzle. The region of the flexible electrode facing the fixed electrode is formed of an oxide film. In the liquid ejecting head, the insulating film is provided with a film thickness of 113 to 138 nm.
In the first aspect, by setting the thickness of the insulating film to 113 to 138 nm, the flexible electrode is repeatedly bent and deformed, thereby preventing the insulating film from being charged due to the insulating film coming into contact with the individual electrode. be able to. As a result, when the flexible electrode is repeatedly bent and deformed, the insulating film can be prevented from sticking to the individual electrode, and the initial stable position can be stabilized to stabilize the droplet discharge characteristics by continuous driving. And durability can be improved. In addition, since a voltage having the same polarity can be repeatedly applied, gradation expression can be expanded.

According to a second aspect of the present invention, in the liquid jet head according to the first aspect, the insulating film is made of silicon oxide.
In the second aspect, the withstand voltage due to the insulating film can be improved, and charging can be prevented.

According to a third aspect of the present invention, in the liquid ejecting head according to the first or second aspect, the insulating film is formed of a dry oxide film formed by dry oxidation.
In the third aspect, the withstand voltage due to the insulating film can be improved, and charging can be prevented.

A fourth aspect of the invention is a liquid ejecting apparatus including the liquid ejecting head according to any one of the first to third aspects.
In the fourth aspect, it is possible to realize a liquid ejecting apparatus that stabilizes droplet discharge characteristics, improves durability, and expands the gradation expression.

Hereinafter, the present invention will be described in detail based on embodiments.
(Embodiment 1)
FIG. 1 is a schematic perspective view of an ink jet recording apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, in the liquid ejecting apparatus, a head unit 200 having an ink jet recording head 210 is detachably provided with cartridges 1A and 1B constituting ink supply means, and a carriage 3 on which the head unit 200 is mounted. Is provided on a carriage shaft 5 attached to the apparatus body 4 so as to be movable in the axial direction. The head unit 200 ejects, for example, a black ink composition and a color ink composition, respectively.

  Then, the driving force of the driving motor 6 is transmitted to the carriage 3 via a plurality of gears and a timing belt 7 (not shown), so that the carriage 3 on which the head unit 200 is mounted is moved along the carriage shaft 5. On the other hand, the apparatus body 4 is provided with a platen 8 along the carriage shaft 5, and a recording sheet S, which is a recording medium such as paper fed by a paper feed roller (not shown), is conveyed on the platen 8. It is like that.

  Here, the ink jet recording head 210 will be described in detail. 2 is an exploded perspective view of the ink jet recording head according to the first embodiment of the present invention, and FIG. 3 is a cross-sectional view of the ink jet recording head.

  As shown in FIGS. 2 and 3, the ink jet recording head 210 is a so-called electrostatic drive head, and includes a cavity substrate 10 and a nozzle plate 20 and an electrode substrate 30 that are respectively bonded to both surfaces of the cavity substrate 10. It consists of and.

  The cavity substrate 10 is made of, for example, a silicon single crystal substrate having a plane orientation (100) or (110), and a plurality of pressure chambers (cavities) 11 opened on one surface side thereof are arranged in parallel in the width direction. Further, the cavity substrate 10 is formed with a common ink chamber 12 which is a common liquid chamber serving as an ink chamber common to the pressure chambers 11. The pressure chamber 11 communicates with the pressure chamber 11. An ink supply hole 13 for supplying ink to the common ink chamber 12 is formed in the bottom wall of the common ink chamber 12. The cavity substrate 10 is formed with a through hole 14 on the outside of the common ink chamber 12 for exposing an individual terminal portion connected to an individual electrode described later. The through hole 14 may be continuously formed up to the end surface of the cavity substrate 10 opposite to the common ink chamber 12.

  The bottom wall of each pressure chamber 11 functions as a diaphragm for causing a pressure change in the pressure chamber 11 and also serves as a common electrode for generating an electrostatic force that displaces the diaphragm. A flexible electrode 15 is formed. In the vicinity of the through hole 14 of the cavity substrate 10, a common terminal portion 16 is formed which is exposed in an exposure hole (described later) of the nozzle plate 20 and connected to a drive wiring (not shown).

  An insulating film 17 made of an oxide film is provided on the surface of the flexible electrode 15 facing the electrode substrate 30 in a region facing the individual electrode 33 of the electrode substrate 30 described later in detail. In the present embodiment, the insulating film 17 is formed over the entire surface of the cavity substrate 10 on the electrode substrate 30 side.

As such an insulating film 17, a dry oxide film formed by dry oxidation is preferable, and silicon dioxide (SiO ₂ ) formed by dry oxidation is particularly preferable. The insulating film 17 can be formed, for example, by thermally oxidizing the cavity substrate 10 made of silicon. The insulating film 17 can be formed on the cavity substrate 10 by TEOS-CVD.

  Such an insulating film 17 is formed with a film thickness of 113 to 138 nm. As will be described in detail later, when the thickness of the insulating film 17 is less than 113 nm, the flexible electrode 15 abuts on the individual electrode 33 when the flexible electrode 15 is repeatedly deformed. Charges are accumulated and charged in the insulating film 17 and the initial stable position of the flexible electrode 15 is deviated or the electric field at the time of energization is affected, so that stable ink ejection characteristics cannot be obtained.

  Further, if the thickness of the insulating film 17 is greater than 138 nm, the rigidity of the flexible electrode 15 is increased, and the electric field strength is reduced, so that the flexible electrode 15 can be deformed as desired. In other words, the amount of displacement decreases and the ink ejection characteristics deteriorate. Therefore, by forming the insulating film 17 with a film thickness of 113 to 138 nm, the initial stable position when the flexible electrode 15 is repeatedly bent and deformed is stabilized, and the ink ejection characteristics by continuous driving are stabilized. And durability can be improved.

  Similarly to the cavity substrate 10, the nozzle plate 20 is made of a silicon single crystal substrate having a plane orientation (100) or (110), and a plurality of nozzles 21 communicating with the pressure chambers 11 are formed. The nozzle plate 20 is bonded to the opening surface side of the cavity substrate 10 to form one surface of the pressure chamber 11 and the common ink chamber 12. A nozzle step portion 22 is formed on the surface of the nozzle plate 20 opposite to the cavity substrate 10 by removing a part in the thickness direction over a region corresponding to the nozzle 21.

  Here, each nozzle 21 is provided on the surface side on which ink droplets are ejected, and has a substantially circular small-diameter portion 21a that opens into the nozzle step portion 22, and a small-diameter portion 21a that has a larger inner diameter than the small-diameter portion 21a. And a large-diameter portion 21 b communicating with the pressure chamber 11. And all the nozzles 21 (small diameter part 21a) are opened in the nozzle level | step difference part 22, and the surface of the nozzle plate 20 in the nozzle level | step difference part 22 turns into a nozzle surface in this embodiment.

  Further, a supply port that communicates each of the pressure chambers 11 and the common ink chamber 12 with a region corresponding to the boundary between the pressure chamber 11 and the common ink chamber 12 is formed on the joint surface of the nozzle plate 20 with the cavity substrate 10. 23 is formed. The supply port 23 is formed by a recess provided on the cavity substrate 10 side of the nozzle plate 20. The nozzle plate 20 is formed with an exposure hole 24 that communicates with the through hole 14 of the cavity substrate 10 at a position corresponding to the outside of the common ink chamber 12 and exposes the common terminal portion 16 together with the individual terminal portion described later. ing. Note that the exposure hole 24 may be formed continuously up to the end surface opposite to the common ink chamber 12, similarly to the through hole 14.

  Further, a water / oil repellent film 25 made of a water / oil repellent material made of, for example, a fluorine-containing silane coupling compound is formed on the surface of the nozzle plate 20, in the present embodiment, in the nozzle step portion 22. Thereby, adhesion of ink droplets to the surface (nozzle surface) of the nozzle plate 20 is suppressed.

  The nozzle 21 and the supply port 23 of the nozzle plate 20 are formed by dry etching the nozzle plate 20.

  On the other hand, the electrode substrate 30 is made of a glass substrate such as borosilicate glass having a thermal expansion coefficient close to that of a silicon single crystal substrate, and is bonded to the surface of the cavity substrate 10 on the flexible electrode 15 side. Grooves 31 corresponding to the pressure chambers 11 are formed in regions of the electrode substrate 30 facing the flexible electrodes 15. In addition, an ink introduction hole 32 communicating with the ink supply hole 13 is formed in the electrode substrate 30 at a position corresponding to the ink supply hole 13 of the cavity substrate 10. Ink is introduced into the common ink chamber 12 from an ink tank (not shown) through the ink introduction hole 32 and the ink supply hole 13.

  Further, in each groove 31, an individual electrode 33, which is a fixed electrode for generating an electrostatic force that displaces each flexible electrode 15, in a state where a predetermined interval is secured between the flexible electrode 15. Each is arranged. Further, in the groove 31, an individual terminal portion 34 to which drive wiring (not shown) is connected is formed in a region facing the through hole 14 of the cavity substrate 10, and the individual terminal portion 34, each individual electrode 33, Are connected by a lead electrode 35. Although not shown, each of the individual electrodes 33 and the flexible electrode 15 is sealed with an insulating film, and a drive voltage pulse is applied between the individual terminal portion 34 and the common terminal portion 16 via a connection wiring. A driver IC (not shown) for application is connected.

  In such an ink jet recording head 210, when a driving voltage is applied between the individual electrode 33 and the flexible electrode 15 by the driver IC, an electrostatic force generated in a gap between the individual electrode 33 and the flexible electrode 15. As a result, the flexible electrode 15 is bent and deformed to the individual electrode 33 side, the volume of the pressure chamber 11 is expanded, and when the application of the drive voltage is released, the flexible electrode 15 returns to the original state and the pressure chamber 11 is restored. The volume of contracts. Then, due to the pressure change in the pressure chamber 11 generated at this time, a part of the ink in the pressure chamber 11 is ejected as an ink droplet from the nozzle 21.

  Here, driving voltage pulses applied between the flexible electrode 15 and the individual electrode 33 of the ink jet recording head 210 will be described with reference to FIGS. 4 to 5 are waveform diagrams showing drive voltage pulses according to the first embodiment of the present invention. The applied voltage of the drive voltage pulse is represented by a pulse voltage V, the application time is represented by a pulse width Pw, and the application period of the drive voltage pulse is represented by a pulse interval Pwi.

  As the drive voltage pulse, for example, as shown in FIGS. 4 to 5, three types of printing one dot pixel are performed by ejecting ink droplets 1 to 3 times within a certain time (for example, 142 μsec). Is mentioned.

  Specifically, as shown in FIG. 4A to FIG. 4C, as the driving voltage pulse, three driving voltage pulses are continuously applied within a predetermined time to eject ink droplets three times. One that performs 3/3 shot printing that prints 1-dot pixels is included. 4A shows a case where the polarity of the drive voltage applied between the flexible electrode 15 and the individual electrode 33 is reversed between forward and reverse, and FIG. 4B shows the polarity of the drive voltage. FIG. 4 (c) shows a case where the polarity of the drive voltage is reversed between forward and reverse.

  Further, as shown in FIGS. 5 (a) and 5 (b), as the drive voltage pulse, two drive voltage pulses are continuously applied within a predetermined time to eject ink droplets twice, thereby causing 1 One that performs 2/3 shot printing that prints dot pixels is included. 5A shows a case where the polarity of the drive voltage applied between the flexible electrode 15 and the individual electrode 33 is reversed between forward and reverse, and FIG. 5B shows a case where the polarity of the drive voltage is reversed. Inverted with positive.

  Further, as shown in FIG. 5C and FIG. 5D, a drive voltage pulse is applied once within a predetermined time as a drive voltage pulse, and an ink droplet is ejected once to form a one-dot pixel. In this case, 1/3 shot printing is performed. FIG. 5C shows the case where the polarity of the drive voltage applied between the flexible electrode 15 and the individual electrode 33 is positive, and FIG. 5D shows the case where the polarity of the drive voltage is reversed. It is.

  As shown in FIGS. 4A to 5B, the driving voltage pulse used in 3/3 shot printing or 2/3 shot printing is generated between the flexible electrode 15 and the individual electrode 33. Since positive and negative voltages are repeatedly applied to the electrodes, even if the flexible electrode 15 contacts the individual electrode 33 and the insulating film 17 is charged, it is canceled and the insulating film 17 is charged. Can be prevented.

  In contrast, as shown in FIGS. 5 (c) and 5 (d), when the driving voltage pulse for 1/3 shot printing is repeatedly applied, only the application of a positive or reverse voltage is continuously performed. Therefore, if 1/3 shot printing is repeated, charging of the insulating film 17 is not canceled and the insulating film 17 is charged.

  Therefore, in the present invention, by setting the thickness of the insulating film 17 to 113 nm or more, the insulating film 17 is charged even when a voltage having the same polarity is repeatedly applied by repeating 1/3 shot printing. It is preventing.

  Here, an endurance test is performed in which a plurality of ink jet recording heads 210 with different film thicknesses of the insulating film 17 are formed, and the ink jet recording head 210 is repeatedly subjected to 1/3 shot printing to measure the incidence of printing defects. went. The result is shown in FIG. Note that 30 inkjet recording heads 210 were simultaneously formed on one silicon wafer with one chip size as shown in FIG. 1 so that the insulating film 17 had the same film thickness. FIG. 6 shows an average value (wafer average: diamond mark), maximum value (wafer MAX: square mark), minimum value (wafer MIN: triangle mark) of the insulating film 17 in the plane of one silicon wafer. The relationship with the printing defect rate is shown.

  Further, in the durability test, 1/3 shot printing was repeatedly performed 13,000 times on each ink jet recording head 210 at an applied voltage V of 34 V, Pw of 7.5 μs, and an environmental temperature of 35 ° C.

  As shown in FIG. 6, when the thickness of the insulating film is thinner than 113 nm, a printing failure occurs. On the other hand, when the insulating film thickness is 113 nm or more, the occurrence of printing failure is prevented. I understand that I can do it.

  If the thickness of the insulating film is thicker than 138 nm, the flexibility of the flexible electrode 15 is increased, and the electric field strength is reduced to allow the flexible electrode 15 to be deformed as desired. In other words, the amount of displacement decreases and the ink ejection characteristics deteriorate. For this reason, by setting the film thickness of the insulating film 17 to 113 to 138 nm, it is possible to prevent charging due to the insulating film 17 coming into contact with the individual electrodes 33 even if the 1/3 shot printing is repeatedly performed. It is possible to stabilize the initial stable position when the flexible electrode 15 is repeatedly bent and deformed, to stabilize ink ejection characteristics by continuous driving, and to improve durability. In addition, since the ink jet recording head 210 can perform printing of four gradations of 3/3 shot printing, 2/3 shot printing, 1/3 shot printing, and non-printing, the gradation expression is expanded. Can do.

(Other embodiments)
As mentioned above, although Embodiment 1 of this invention was demonstrated, the basic composition of this invention is not limited to what was mentioned above.

  For example, in Embodiment 1 described above, the insulating film 17 is formed over the entire surface of the cavity substrate 10 on the electrode substrate 30 side. However, the present invention is not limited to this, and the insulating film 17 is at least a flexible electrode. 15 should just be provided in the area | region which contact | abuts to the individual electrode 33, and should just be provided in the area | region which opposes the individual electrode 33 of the flexible electrode 15. FIG.

In Embodiment 1 described above, silicon dioxide is exemplified as the material of the insulating film 17, but is not particularly limited as long as it is an oxide film having a withstand voltage. For example, zirconium oxide (ZrO ₂ ) or the like is used. You can also

  Furthermore, in the first embodiment described above, an ink jet recording head that ejects ink droplets as a liquid ejecting head has been described as an example. However, the present invention can be widely applied to all liquid ejecting heads. For example, as a liquid ejecting head, for forming electrodes such as a recording head used in an image recording apparatus such as a printer, a color material ejecting head used for manufacturing a color filter such as a liquid crystal display, an organic EL display, and an FED (field emission display). An electrode material ejecting head used, a bioorganic matter ejecting head used for biochip production, or the like can be applied.

1 is a schematic perspective view of an ink jet recording apparatus according to Embodiment 1 of the present invention. FIG. 2 is an exploded perspective view of a recording head according to Embodiment 1 of the invention. FIG. 3 is a cross-sectional view of the recording head according to the first embodiment of the invention. It is a wave form diagram which shows the drive voltage pulse which concerns on Embodiment 1 of this invention. It is a wave form diagram which shows the drive voltage pulse which concerns on Embodiment 1 of this invention. It is a graph which shows the endurance test result concerning Embodiment 1 of the present invention.

Explanation of symbols

  1A, 1B cartridge, 3 carriage, 10 cavity substrate, 11 pressure chamber, 12 common ink chamber, 14 through hole, 15 flexible electrode, 17 insulating film, 20 nozzle plate, 21 nozzle, 21a small diameter portion, 21b large diameter portion , 22 nozzle step, 23 supply port, 24 exposure hole, 25 water / oil repellent film, 30 electrode substrate, 31 groove, 33 individual electrode, 200 head unit, 210 ink jet recording head

Claims (4)

A plurality of pressure chambers communicating with a nozzle from which liquid droplets are ejected; a flexible electrode provided on one surface of the pressure chamber; and a fixed electrode disposed to face the flexible electrode at a predetermined interval. Then, a driving voltage pulse is applied between the flexible electrode and the fixed electrode, and the flexible electrode is vibrated by an electrostatic force generated between them, thereby generating a pressure fluctuation in the pressure chamber. A liquid ejecting head for ejecting liquid droplets from the nozzle,
In the liquid jet head, an insulating film made of an oxide film having a thickness of 113 to 138 nm is provided in a region of the flexible electrode facing the fixed electrode. The liquid ejecting head according to claim 1, wherein the insulating film is made of silicon oxide. The liquid ejecting head according to claim 1, wherein the insulating film is made of a dry oxide film formed by dry oxidation. A liquid ejecting apparatus comprising the liquid ejecting head according to claim 1.

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