JP5715345B2 - Liquid discharge head - Google Patents

Description

The present invention relates to a liquid ejection head, in particular, relates to a liquid discharge head having a function of cleaning the inside of the liquid ejection head.

  In general, as a general-purpose image forming apparatus, an ink jet recording apparatus that forms a desired image by ejecting ink droplets from an ink jet head onto a recording medium is widely used. In an ink jet recording apparatus, abnormal discharge may occur due to bubbles in a flow path inside an ink jet head or clogging with solid foreign matter. When the ejection abnormality occurs, there is a problem that the image quality is remarkably deteriorated, for example, unevenness occurs in the recorded image.

  As a method for defoaming or cleaning bubbles in the flow path of the inkjet head, for example, in Patent Document 1 below, a common piezoelectric material for vibrating a flow path wall is used in addition to the piezoelectric material for ink ejection. It describes that it is arranged on the outer wall of the liquid chamber to defoam the ink.

  Further, Patent Document 2 has a cap including an ultrasonic vibrator that covers the discharge port of the discharge nozzle, and cleaning is performed using ultrasonic waves, so that the solid matter in the nozzle hole, the nozzle plate surface, It describes the removal of deposits. Patent Document 3 describes that the aggregates in the nozzles can be efficiently removed by oscillating ultrasonic waves having a frequency of 700 kHz or more and jetting a cleaning liquid excited in a direction opposite to the ink ejection direction. .

JP-A-10-119265 JP 2006-347000 A JP 2005-028758 A

  As described above, the inkjet head or the liquid ejection device described in Patent Documents 1 to 3 has proposed a method of cleaning the nozzle by using ultrasonic waves by capping or jet cleaning outside the nozzle. Also, in order to prevent clogging of bubbles in the flow path inside the head and clogging of foreign solids, a piezoelectric body that is different from the piezoelectric body for ink ejection is placed near the flow path to generate ultrasonic waves for maintenance. It has been proposed to do so.

  However, the arrangement of external units such as an ultrasonic cap unit and an ultrasonic jet cleaning unit has led to a significant complication of the system configuration. In addition, when the piezoelectric bodies are individually arranged on the flow path, not only the structure is complicated, but also a great obstacle to the progress of high density miniaturization such as a small high-definition discharge head.

The present invention has been made in view of such circumstances, and provides a liquid discharge head having a simple configuration and capable of eliminating air bubbles in a flow path and a nozzle part or maintaining clogging of foreign substances.

A liquid discharge head for achieving the object of the present invention is provided on a nozzle that discharges a liquid, a pressure chamber that communicates with the nozzle and stores a liquid discharged from the nozzle, and a wall surface that forms the pressure chamber. A piezoelectric actuator that pressurizes the liquid in the pressure chamber, the piezoelectric actuator including a diaphragm, a lower electrode formed on an upper surface of the diaphragm, and a side of the lower electrode opposite to the diaphragm A piezoelectric film formed on the upper surface of the piezoelectric film, an upper electrode formed on the side surface of the piezoelectric film opposite to the lower electrode, and a restraint plate provided on the side surface of the upper electrode opposite to the piezoelectric film. And a constraining plate in which a portion located above the nozzle is opened, and the vibration plate, the lower electrode, and the piezoelectric film are formed without using an adhesive, The piezoelectric actuator is Combines an ultrasonic oscillation function part is constrained by the constraining plate is ultrasonically oscillated in d ₃₃ mode, and a circuit for the ejection driving for ejecting the liquid and the two driving circuits of the circuit for ultrasonic oscillation And a control circuit for controlling each of the drive circuits, the film thickness of the piezoelectric film constituting the piezoelectric actuator is 5 μm or more and 15 μm or less, and the d ₃₃ mode ultrasonic frequency is 100 MHz or more .

According to the present invention , by providing the piezoelectric actuator with an ultrasonic oscillation function, it is possible to oscillate ultrasonic waves using the piezoelectric actuator that discharges ink and to clean the inside of the droplet discharge head. Accordingly, it is not necessary to add a separate structure for cleaning, and thus the complexity of the apparatus and the increase in cost can be prevented.
In addition, by setting the film thickness of the piezoelectric film within the above range, high-frequency ultrasonic waves can be oscillated. Further, the liquid ejection head can be reduced in size by reducing the film thickness.
In addition, by setting the d ₃₃ mode ultrasonic frequency within the above range, the liquid discharge head can be effectively cleaned and the bubbles can be removed.
In addition, since the piezoelectric actuator is driven using two types of drive circuits and a control circuit, the drive system circuit of the piezoelectric body can be easily changed.
In addition, since the diaphragm, lower electrode, and piezoelectric film are formed without using an adhesive, air or the like is not mixed in between them, and ultrasonic waves can be efficiently transmitted into the pressure chamber. Therefore, it can wash effectively.

  According to the liquid discharge head and the liquid discharge head cleaning method of the present invention, the inside of the droplet discharge head can be cleaned using the piezoelectric film for ink discharge, so that the cleaning can be performed without adding a new structure. It is possible to prevent the apparatus from becoming complicated and increasing in cost.

It is a figure explaining the board | substrate with which a piezoelectric material actuator is formed. It is a figure explaining a lower electrode formation process. It is a figure explaining the patterning process of a lower electrode. It is a figure explaining a piezoelectric material film formation process. It is a figure explaining an upper electrode formation process. It is a figure explaining the patterning process of an upper electrode. It is a figure explaining a restraint board film-forming process. It is a figure explaining a restraint board film-forming process. It is a figure explaining a pressure chamber formation process. It is a figure explaining a channel plate joining process and a nozzle plate joining process. It is a conceptual diagram of the drive circuit of a liquid discharge head.

  Hereinafter, preferred embodiments of a liquid discharge head and a method for cleaning a liquid discharge head according to the present invention will be described with reference to the accompanying drawings.

[Description of Manufacturing Method of Liquid Discharge Head]
A method for manufacturing a liquid ejection head according to an embodiment of the present invention will be described with reference to FIGS.

(1) Lower Electrode Formation Step FIG. 1 shows an SOI substrate (a silicon substrate provided with an insulating film of SiO ₂ , hereinafter referred to as a substrate) 110 which is a surface insulating substrate. The substrate 110 shown in FIG. 1 has a structure in which a silicon base 111, an insulating layer 112 made of a silicon oxide film, a silicon base 114, and an insulating layer 116 made of a silicon oxide film are stacked in order from the bottom. ing.

  FIG. 2 shows a state in which a metal film 118 serving as a lower electrode is formed on the substrate 110 shown in FIG. A metal film 118 serving as a lower electrode is formed on the upper surface of the substrate 110 (the surface on which the insulating layer 116 is formed) using a technique such as sputtering or vapor deposition. Thereafter, as shown in FIG. 3, the metal film 118 is processed into a predetermined shape using reactive ion etching (RIE). For the metal film (lower electrode) 118, iridium (Ir), platinum (Pt), titanium (Ti), or the like is preferably used.

  The arrangement pattern of the lower electrode 118 is an arrangement pattern of a piezoelectric actuator including a piezoelectric element (structure denoted by reference numeral 125 in FIGS. 8 to 10), and ink is ejected according to the arrangement pattern of the piezoelectric actuator. (Shown by reference numeral 124 in FIG. 10) is arranged. In other words, the arrangement pattern of the lower electrode 118 is determined corresponding to the arrangement of nozzles and pressure chambers that eject ink.

(2) Piezoelectric film forming step When the lower electrode (metal film) 118 is processed into a predetermined shape (pattern), the surface on the upper side of the lower electrode 118 (on the side opposite to the insulating layer 116 of the lower electrode 118) The piezoelectric film 120 having orientation is formed using a thin film formation process by an epitaxial growth method such as sputtering, CVD, or sol-gel. PZT (lead zirconate titanate, Pb (Zr, Ti) O ₃ ) is preferably used for the piezoelectric film 120. FIG. 4 illustrates a state in which the piezoelectric film 120 is formed.

(3) Upper electrode film forming step When the piezoelectric film 120 is formed, a method such as sputtering or vapor deposition is applied to the upper surface of the piezoelectric film 120 (on the side opposite to the lower electrode 118 of the piezoelectric film 120). A metal film 122 that serves as an upper electrode is formed. For the metal film (upper electrode) 122, iridium (Ir), platinum (Pt), titanium (Ti), gold (Au), or the like is preferably used. FIG. 5 illustrates a state where a metal film 122 serving as an upper electrode is formed.

  Thereafter, as shown in FIG. 6, the metal film (upper electrode) 122 is patterned into a predetermined shape. Etching is preferably used for patterning the upper electrode 122 and patterning the lower electrode 118, and the patterning (etching process) of the upper electrode 122 (lower electrode 118) is performed at a temperature of about 150 ° C.

(4) Constraining Plate Film Formation Step Next, a constraining plate 123 is formed on the side surface of the upper electrode 122 opposite to the piezoelectric film 120. A thin film forming technique such as sputtering or CVD is used for forming the constraining plate 123, and a metal oxide such as SiO ₂ , Al ₂ O ₃ , or ZrO ₂ is used as a material for the constraining plate 123.

(5) Wiring Layer Formation Step When the constraining plate 123 is formed, the portion of the constraining plate 123 and the piezoelectric film 120 from which the lower electrode 118 is taken out is removed by etching (wiring layer forming step). The wiring layer forming step is performed at a temperature of 200 ° C. to 350 ° C. Illustration of the wiring layer forming step is omitted.

(6) Restraint Plate Etching Step Next, the restraint plate 123 at a portion (a portion where an FPC to be described later is joined) from which the upper electrode 122 is taken out is removed by etching. FIG. 8 illustrates a state where the restraint plate 123 is removed and a part of the upper electrode 122 is exposed.

(7) Pressure Chamber Formation Step Next, an opening (shape) 124 to be a pressure chamber is formed in the silicon base material 111 using a technique such as etching. FIG. 9 illustrates a state in which an opening 124 serving as a pressure chamber is formed.

(8) Flow path substrate bonding step and nozzle substrate bonding step As shown in FIG. 9, when the pressure chamber 124 is formed, a structure (an ink flow path is formed on the side of the substrate 110 where the pressure chamber 124 is formed). A flow path substrate 126 having a groove, a hole, etc.) is joined. When the substrate 110 and the flow path substrate 126 are joined, the ink flow path and the pressure chamber 124 are accurately aligned.

  Further, the nozzle substrate 128 in which the fine holes 127 to be nozzles are formed is bonded to the side opposite to the substrate 110 of the flow path substrate 126 to form the liquid discharge head structure 129. When the nozzle substrate 128 and the flow path substrate 126 are joined, the fine hole 127 and the discharge side flow path are accurately aligned. FIG. 10 illustrates a state in which the flow path substrate 126 and the nozzle substrate 128 are joined.

  In the above-described method, the method of forming a film on the substrate by a method such as sputtering or vapor deposition has been described. However, the liquid discharge head of the present invention is not limited to this, and bulk baking formed in a bulk shape by sintering is performed. It is also possible to manufacture the bonded piezoelectric body by adhering it to the head casing (silicon) with an adhesive or the like.

  However, in the present invention, high-frequency ultrasonic waves are oscillated to clean the inside of the liquid discharge head. Generally, when air or the like is present between them, the ultrasonic waves are almost 100% reflected and cannot be transmitted. In particular, bubbles in the adhesive are an obstacle.

  Therefore, as described above, the ultrasonic conductivity to the casing material can be improved by directly forming the piezoelectric film on the casing substrate forming the pressure chamber.

  In addition, the acoustic conduction characteristics of the ultrasonic waves are highly influenced by the acoustic impedance (= density × sound speed) of the material. Ultrasonic reflection occurs between materials having greatly different acoustic impedances, and efficient ultrasonic conduction is difficult. For example, when a silicon substrate is used for the casing, the arrangement of silicon, metal electrode, and piezoelectric body is adopted, and the acoustic impedance value becomes close, so that efficient ultrasonic conduction can be realized. Since a low density resin material or the like has low acoustic impedance, it is difficult to efficiently conduct ultrasonic waves from the piezoelectric body to the casing (silicon) when the piezoelectric body is made of resin.

  Therefore, an ultrasonic wave can be effectively conducted by producing a liquid discharge head using a material having a close acoustic impedance without using an adhesive.

[Liquid discharge head drive circuit]
FIG. 11 is a conceptual diagram of the driving circuit 1 for the liquid discharge head.

  In the present invention, the piezoelectric body for ink ejection is used not only for ink ejection but also as a piezoelectric body for ultrasonic transmission for maintenance. Accordingly, the liquid discharge head can be cleaned by ultrasonically oscillating the piezoelectric body in the maintenance mode in which the ink discharge is stopped.

  In normal ultrasonic cleaning (several tens of kHz), dirt, ink solids, bubbles, and the like are removed mainly by a cavitation action caused by a change in sound pressure generated in the liquid. In this case, since a constant material wave corresponding to the frequency is generated, cleaning unevenness and removal unevenness are likely to occur.

  The above problem can be avoided by increasing the frequency. The drive circuit for ejection drive can only support frequencies up to about 2 MHz. Therefore, in the present invention, as shown in FIG. 11, for the purpose of maintenance, the ultrasonic drive circuit unit 20 is provided and driven when ink discharge is stopped, thereby cleaning the liquid discharge head. It is preferable to use an ultrasonic drive circuit unit 20 compatible with 300 MHz. As shown in FIG. 11, the ultrasonic drive circuit unit 20 can be provided in parallel with the ejection drive circuit unit 10. The channel control IC (ASIC) 30 to the piezoelectric body can be shared, and the wiring configuration from the ASIC 30 to the piezoelectric body can be shared. Then, the ASIC 30 controls which waveform the oscillating waveform generated by the ejection driving circuit unit 10 and the ultrasonic driving circuit unit 20 is driven. Accordingly, only the ejection driving circuit unit 10 is operated during ejection driving, and the liquid ejection head can be cleaned by switching to the ultrasonic driving circuit unit 20 only during ultrasonic oscillation. In FIG. 11, only one piezoelectric body (PZT) is shown, but a plurality of piezoelectric bodies are controlled by one ASCI.

  As another method for driving the piezoelectric body, an individual connection switch is provided between the drive circuit section and the piezoelectric body, and a discharge drive circuit section, an ultrasonic drive circuit section, and a control circuit for controlling the individual connection switches are provided. Cleaning can also be performed by controlling the piezoelectric body and waveform provided and driven by the control circuit.

The thickness of the piezoelectric film is preferably 5 μm or more and 15 μm or less, and more preferably 5 μm or more and 10 μm or less. The resonance frequency of the ultrasonic wave is inversely proportional to the thickness of the piezoelectric film, and can be increased as the piezoelectric film becomes thinner. For example, the thickness in the case of 10 MHz is 150 μm, 15 μm at 100 MHz, and 1.5 μm at 1 GHz, whereby high-frequency ultrasonic waves can be oscillated. In addition, by using a higher frequency, damage to the head casing can be reduced, and cleaning properties can be improved. However, in general, if the piezoelectric film is formed to exceed 15 μm due to film stress, cracks and peeling problems are likely to occur. Therefore, the film thickness is preferably 15 μm or less. In the case of a 15 μm thick piezoelectric film, the d ₃₃ mode ultrasonic oscillation frequency is 100 MHz as described above, and the oscillation ultrasonic frequency is preferably 100 MHz or more.

Further, when the liquid discharge head is a high-resolution small head, it is necessary to ensure a large displacement with a small pressure chamber area, so it is preferable to reduce the thickness of the driving piezoelectric film. Therefore,
By thinning the piezoelectric film, it can be suitably used as a driving piezoelectric film and a maintenance piezoelectric film.

  As described above, by sharing the piezoelectric body arranged as the driving piezoelectric body as the ultrasonic oscillating element for maintenance, a large additional structure and cost other than the ultrasonic driving circuit and the power source are not required. In particular, in the case of a high-density small head, since the degree of freedom in design is small, it is effective to use a piezoelectric body in common.

[Example]
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited thereto.

As a film formation substrate, an electrode substrate in which a 30 nm thick Ti adhesion layer and a 150 nm thick Pt lower electrode were sequentially laminated on an SOI wafer was prepared. Next, a PZT piezoelectric film having a thickness of 5 μm was formed by an RF sputtering apparatus using a Pb _1.3 Zr0.52Ti _0.48 O ₃ target. The film forming conditions are as follows.

Substrate temperature: 525 ° C
Target applied voltage: 2.5 W / cm ²
Distance between substrate and target: 60mm
Degree of vacuum: 0.5Pa
Deposition gas: Ar / O ₂ mixed gas (O ₂ partial pressure 1.3 mol%)
Thereafter, the upper electrode was patterned by a normal photolithography method. The upper electrode has a stacked structure of a 50 nm thick Ti layer and a 200 nm thick Pt layer. Thereafter, a Si sacrificial substrate was directly pressure bonded to the upper electrode side. Next, the back surface side of the SOI substrate was subjected to reactive ion etching to the SiO ₂ stop layer to form a concave structure serving as a diaphragm and a pressure chamber. The thickness of the diaphragm was about 10 μm.

  Next, an ink discharge structure was formed by bonding a silicon plate having a nozzle hole processed to the concave structure side.

When the manufactured liquid discharge head was used and the PZT thin film was used for driving for ink discharge, the discharge operation was performed at an applied voltage of 30 V and a frequency of 100 kHz. On the other hand, when used for driving for maintenance, it was operated at a frequency of 300 MHz. (Since the thickness of the PZT thin film is 5 μm, the oscillating frequency is 300 MHz.)
When 10 billion pulses of ink were continuously ejected, solidified ink and bubbles were generated in the vicinity of the nozzle and in the pressure chamber, and a defective ejection nozzle was confirmed.

  On the other hand, when about 100 million pulses were operated, 100 minutes of ultrasonic oscillation for 1 minute was operated as a maintenance mode as a cycle (discharge operation 10 billion pulses), and then ink was discharged. No nozzles with poor discharge due to bubbles were found.

  DESCRIPTION OF SYMBOLS 1 ... Drive circuit part, 10 ... Discharge drive circuit part, 20 ... Ultrasonic drive circuit part, 30 ... Channel control IC, 110 ... Substrate, 118 ... Metal film (lower electrode), 120 ... Piezoelectric film, 122 DESCRIPTION OF SYMBOLS ... Metal film (upper electrode), 123 ... Restraint plate, 124 ... Pressure chamber, 125 ... Piezoelectric actuator, 126 ... Flow path substrate, 127 ... Fine hole (nozzle), 128 ... Nozzle substrate, 129 ... Liquid discharge head structure ,

Claims (1)

A nozzle for discharging liquid;
A pressure chamber communicating with the nozzle and containing a liquid discharged from the nozzle;
A piezoelectric actuator provided on a wall surface constituting the pressure chamber and pressurizing a liquid in the pressure chamber; and
The piezoelectric actuator includes a vibration plate, a lower electrode formed on the upper surface of the vibration plate, a piezoelectric film formed on the upper surface of the lower electrode on the side opposite to the vibration plate, and the piezoelectric film An upper electrode formed on a side surface opposite to the lower electrode, and a constraint plate provided on a side surface opposite to the piezoelectric film of the upper electrode and having a portion opened above the nozzle opened. The diaphragm, the lower electrode, and the piezoelectric film are formed without using an adhesive,
The piezoelectric actuator has both ultrasonic oscillation function part is constrained by the constraining plate is ultrasonically oscillated in d ₃₃ mode,
Two types of drive circuits, a discharge drive circuit for discharging the liquid and a circuit for ultrasonic oscillation, and a control circuit for controlling each of the drive circuits,
The film thickness of the piezoelectric film constituting the piezoelectric actuator is 5 μm or more and 15 μm or less,
d A liquid ejection head characterized by having a _33- mode ultrasonic frequency of 100 MHz or more.

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