KR20070078206A - Driving nethod of ink-jet printhead adopting piezoelectric actuator - Google Patents

Abstract

A method of driving an inkjet print head adopting a piezoelectric actuator is provided to improve the usage rate of ink by discharging the ink droplet with the same size at an initial stage of printing. A method of driving an inkjet print head adopting a piezoelectric actuator includes the steps of changing the volume of a pressure chamber using the piezoelectric actuator, generating discharging pressure, and discharging ink through a nozzle. The volume of a discharged ink droplet is uniformly maintained by applying an initial driving pulse having a form changing at least one of a driving voltage and duration time(d1) to the piezoelectric actuator until the position of a meniscus inside of the nozzle is stabilized during the initial stage of printing.

Description

Driving method of inkjet printhead employing piezoelectric actuators {Driving nethod of ink-jet printhead adopting piezoelectric actuator}

1A to 1C are views for explaining a reduction in the size of ink droplets in accordance with a conventional method for driving a piezoelectric inkjet printhead.

Figure 2 is a vertical cross-sectional view showing an example of the structure of a piezoelectric inkjet printhead applied to the driving method of the present invention.

3 is a view showing the shape of a driving pulse according to a first embodiment of a method of driving a piezoelectric inkjet printhead according to the present invention;

4 is a graph showing the behavior of a piezoelectric film according to a change in a driving voltage of a driving pulse.

5 is a view showing the shape of a driving pulse according to a second embodiment of a method of driving a piezoelectric inkjet printhead according to the present invention;

6 is a graph showing the behavior of a piezoelectric film with a change in the duration of a driving pulse.

7 is a view showing the shape of a driving pulse according to a third embodiment of the method for driving a piezoelectric inkjet printhead according to the present invention;

<Explanation of symbols for the main parts of the drawings>

110 ... Euro-forming substrate 111 ... Pressure chamber

112 ... Lister 113 ... Manifold

114 ... vibration plate 120 ... nozzle board

122 Nozzle 131 Silicon Oxide

140 Piezoelectric actuator 141 Lower electrode

142 Piezoelectric Film 143 Top Electrode

The present invention relates to a method of driving an inkjet printhead, and more particularly, to a method of driving an inkjet printhead for ejecting ink by a piezoelectric method.

In general, an inkjet printhead is an apparatus for ejecting a small droplet of printing ink to a desired position on a recording sheet to print an image of a predetermined color. Such inkjet printheads can be classified into two types according to ink ejection methods. One is a heat-driven inkjet printhead that generates bubbles in the ink by using a heat source and discharges the ink by the expansion force of the bubbles. The other is a piezoelectric inkjet printhead. It is a piezoelectric inkjet printhead which discharges ink by an applied pressure.

The piezoelectric inkjet printhead includes an ink flow path including a manifold constituting an ink flow path, a plurality of restrictors, and a plurality of pressure chambers, a plurality of nozzles in communication with the plurality of pressure chambers, and a plurality of discharge pressures in the pressure chambers. It is provided with a piezoelectric actuator. The manifold is a passage for supplying ink flowing from the ink reservoir to the plurality of pressure chambers. The restrictor is a passage through which ink flows from the manifold into the pressure chamber. The pressure chamber is where the ink to be ejected is filled. The pressure chamber causes the piezoelectric actuator to change the pressure of the ink by changing the volume of the pressure chamber.

1A, 1B and 1C show the state of the meniscus of the nozzle in the initial state of starting printing and the size of the ejected ink droplets. Referring to Fig. 1A, in the case where the printing operation is not performed, it reaches the tip of the nozzle of the meniscus. When a driving pulse is applied to the piezoelectric actuator, ink droplets are ejected through the nozzle. The meniscus then returns to the state shown in FIG. 1A as the ink enters the pressure chamber. Again, when a driving pulse having the same duration and driving voltage is applied to the piezoelectric actuator, ink droplets of the same size are ejected.

There is no flow of ink through the ink flow path while the print job is not being performed. In the early stage of printing, ink cannot be rapidly filled in the pressure chamber and the nozzle due to the influence of the flow resistance in the ink flow path and the inertia of the ink due to the viscosity of the ink. Thus, the meniscus is slightly retracted from the tip of the nozzle as shown in FIG. 1B. In this state, when a driving pulse having the same duration and driving voltage is applied to the piezoelectric actuator again, the size of the ejected ink droplet is reduced. The meniscus is further retracted from the tip of the nozzle as shown in FIG. 3C. In this state, when the driving pulse having the same duration and driving voltage is applied to the piezoelectric actuator again, the size of the ejected ink droplet is smaller. .

SUMMARY OF THE INVENTION The present invention has been made in view of the necessity as described above, and an object thereof is to provide a method for driving a piezoelectric inkjet printhead capable of ejecting ink droplets of uniform size.

The piezoelectric inkjet printhead driving method of the present invention for achieving the above object is a piezoelectric inkjet printhead of the piezoelectric inkjet printhead for generating a discharge pressure by changing the volume of the pressure chamber using a piezoelectric actuator to discharge ink through the nozzle In the driving method, the ink liquid discharged by applying to the piezoelectric actuator an initial driving pulse of a form in which at least one of the driving voltage and its duration is changed until the position of the meniscus in the nozzle is stabilized at the beginning of printing. It is characterized by maintaining a constant volume of the enemy.

In one embodiment, the duration of the initial drive pulse is fixed and the drive voltage is gradually increased.

In one embodiment, the driving voltage of the initial driving pulse is fixed, and the duration is gradually increased.

In one embodiment, the product of the driving voltage and the delay time of the initial driving pulse is gradually increased.

In one embodiment, the number of the initial driving pulses is preferably within 10.

In one embodiment, after the position of the meniscus in the nozzle is stabilized, a driving pulse having a last driving voltage and a duration is applied to the piezoelectric actuator.

In the drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of description. In addition, when one layer is described as being on top of a substrate or another layer, the layer may be present over and in direct contact with the substrate or another layer, with a third layer in between. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a vertical cross-sectional view of an embodiment of a piezoelectric inkjet printhead to which a driving method according to the present invention is applied.

Referring to FIG. 2, the piezoelectric inkjet printhead includes a flow path forming substrate 110 on which an ink flow path is formed, and a safety actuator 140 for providing an ink discharge pressure. The flow path forming substrate 110 is provided with a pressure chamber 111, a manifold 113 and a restrictor 112 for supplying ink to the pressure chamber 111. A nozzle substrate 120 having a nozzle 122 communicating with the pressure chamber 111 and discharging ink is bonded to the flow path forming substrate 110. An upper portion of the pressure chamber 111 is provided with a diaphragm 114 that is deformed by the driving of the piezoelectric actuator 140. An ink flow path is defined by the flow path forming substrate 110 and the nozzle substrate 120.

The piezoelectric actuator 140 is formed on the flow path forming substrate 110 to provide a driving force for discharging ink to the pressure chamber 111. The piezoelectric actuator 140 includes a lower electrode 141 serving as a common electrode, a piezoelectric film 142 deformed by application of a voltage, and an upper electrode 143 serving as a driving electrode. The electrode 141, the piezoelectric film 142, and the upper electrode 143 are sequentially stacked on the flow path forming substrate 110.

The lower electrode 141 is formed on the flow path formation substrate 110 on which the pressure chamber 111 is formed. When the flow path formation substrate 110 is formed of a silicon wafer, a silicon oxide film 131 may be formed as an insulating layer between the flow path formation substrate 110 and the lower electrode 141. The lower electrode 141 is made of a conductive metal material. The lower electrode 141 may be formed of one metal layer. It is preferable that it consists of two metal layers, a Ti layer and a Pt layer. The lower electrode 141 made of a Ti / Pt layer not only functions as a common electrode, but also inter-diffusion between the piezoelectric layer 142 formed thereon and the flow path forming substrate 110 thereunder. It also serves as a diffusion barrier layer to prevent.

The piezoelectric film 142 is formed on the lower electrode 141 and is disposed at a position corresponding to the pressure chamber 111. The piezoelectric film 142 may be formed of a piezoelectric material, preferably, a lead zirconate titanate (PZT) ceramic material. The piezoelectric film 142 is formed by applying a piezoelectric material in a paste state to a predetermined thickness on the silicon oxide film 131 by screen printing.

The bonding pad 144 is for electrically connecting the upper electrode 143 and the driving circuit for voltage application, for example, the flexible printed circuit 150, and the wiring 151 of the flexible printed circuit 150 is bonded on the upper surface thereof. do. The bonding pad 144 is disposed to be adjacent to the pressure chamber 111, and is formed to be insulated from the lower electrode 131 on the same plane as the lower electrode 141, that is, on the silicon oxide film 131. The bonding pad 144 and the lower electrode 141 may be made of the same material. The bonding pad 114 is surrounded by the trench 134 formed to penetrate the lower electrode 141 and insulated from the lower electrode 141. The width of the bonding pad 144 may be defined to be wider than the width of the upper electrode 143, preferably larger than the width of the piezoelectric film 142. The bonding pads 144 are formed of a conductive metal material.

The upper electrode 143 serves as a driving electrode for applying a voltage to the piezoelectric film 142 and is formed on the piezoelectric film 142 and extends to the bonding pad 144. A driving pulse for driving the piezoelectric actuator is applied to the upper electrode 143 through the flexible printed circuit 150.

The structure of the flow path forming substrate 110, the nozzle substrate 120, and the piezoelectric actuator 140 shown in FIG. 2 is just one example. That is, the piezoelectric inkjet printhead may be provided with ink passages having various structures, and the ink passages may be formed using a plurality of substrates rather than the two substrates 110 and 120 shown in FIG. 3. It may be. In addition, the structure of the piezoelectric actuator 140 and the connection structure for applying a driving pulse to the piezoelectric actuator may be modified into various structures. In other words, the present invention is not characterized by the structure of the ink flow path, the structure of the piezoelectric actuator 140, the structure for connecting the piezoelectric actuator and the driving circuit for voltage application, and the size of the ink droplets discharged at the beginning of printing. It is known in advance that the driving method for maintaining the same has its features.

When the driving pulse is applied to the upper electrode 143, the length of the piezoelectric film 142 is changed, thereby vibrating the diaphragm 114 to change the volume of the pressure chamber 111. The ink in the pressure chamber 111 is discharged through the nozzle 122 by this volume change. In the beginning of printing, ink is not rapidly filled in the pressure chamber 111 and the nozzle 122 due to the influence of flow resistance in the ink flow path and ink inertia due to the viscosity of the ink. Therefore, when a driving pulse having a constant driving voltage and a duration is applied to the upper electrode 143, the size of the ink droplets ejected gradually decreases as shown in FIGS. 1A to 1C. The decrease in the size of the ink droplets is more severe the higher the viscosity of the ink and the higher the frequency of the driving pulse. In order to realize a high quality printed image by high speed printing, the ejected ink droplets must have a constant size. In recent years, inkjet printing has been applied to the manufacturing process of the color filter of the liquid crystal display device, the manufacturing process of the light emitting layer of the organic light emitting diode (OLED), and the manufacturing process of the organic thin film transistor (OTFT). In addition, since the ink used in the above-described manufacturing process contains pigments for color filters, organic light emitting materials, and semiconductor materials, the ink has a higher viscosity than the ink used for office inkjet printers. In addition, attempts have been made to increase the frequency of the drive pulses in order to cope with high speed of the manufacturing process. Therefore, high uniformity of the size of the ink droplets is required.

In this manner, the initial printing is defined until the ink droplet becomes constant. The driving method according to the present invention is characterized in that the ink droplets of a predetermined size can be discharged even in the initial printing stage by changing the voltage and the duration of the driving pulse applied at the beginning of printing.

As a first embodiment of the driving method according to the present invention, as shown in FIG. 3, the duration d1 of the driving pulse is constant at the beginning of printing, and the driving voltage V ₁ <V ₂ <V ₃ is maintained. You might consider increasing it gradually. The driving voltage is related to the strain rate and the magnitude of the displacement of the piezoelectric film 142. 4 is a graph showing the relationship between the drive voltage of the drive pulse and the displacement of the piezoelectric film 142. Referring to FIG. 4, as the driving voltage V ₁ <V ₂ <V ₃ increases, the deformation speed of the piezoelectric layer 142 increases and the displacement increases. As the displacement of the piezoelectric film 142 increases, the volume change of the pressure chamber 111 increases, and the size of the ink droplets that are ejected increases. To enable printing to when the driving pulse applied to the (PV1) drive voltage V ₁ (for example, 60V), the duration (d1 = 4㎲) the first ink droplet is ejected. The meniscus is then slightly retracted from the tip of the nozzle 122 as shown in FIG. 1B. When the driving pulse PV1 is applied again in this state, the size of the ink droplet is reduced as shown in Fig. 1B. However, according to the driving method of the present embodiment, the driving pulse PV2 having the driving voltage of V ₂ (for example, 65 V) is applied. Then, the displacement of the piezoelectric film 142 applies the driving voltage PV1. The ink droplets are larger than usual to increase the size of the ejected ink droplets, that is, the displacement of the piezoelectric film 142 is increased to compensate for the size of the ink droplets reduced by the retreat of the meniscus. The size of the droplet can be made approximately equal to the size of the first ejected ink droplet After the second ink droplet is ejected, the meniscus is further retracted from the tip of the nozzle 122 again as shown in Fig. 1C. By applying a driving pulse PV3 having a driving voltage of V ₃ (for example, 70 V), it is possible to discharge the ink droplets of the same size three times by compensating the size of the ink droplets reduced by the retreat of the meniscus. .

As a second embodiment of the driving method according to the present invention, as shown in Fig. 5, in the initial stage of printing, the driving voltage V ₁ of the driving pulse is made constant and the duration d ₁ <d ₂ <d ₃ is set. You might consider increasing it gradually. FIG. 6 is a graph showing the relationship between the driving time duration d ₁ <d ₂ <d ₃ and the displacement of the piezoelectric film 142. Referring to FIG. 6, as the duration d ₁ <d ₂ <d ₃ increases, the displacement of the piezoelectric film 142 increases. As the displacement of the piezoelectric film 142 increases, the volume change of the pressure chamber 111 increases, and the size of the ink droplets that are ejected increases. When the printing is started and a driving pulse PD1 having a driving voltage of V ₁ (for example, 60 V) and a duration d1 = 4 kW is applied, the first ink droplet is ejected. The meniscus is then slightly retracted from the tip of the nozzle 122 as shown in FIG. 1B. When the driving pulse PD1 is applied again in this state, the size of the ink droplet is reduced as shown in Fig. 1B. However, according to the driving method of this embodiment, a driving pulse PD2 having a duration of d ₂ (for example, 5 kW) is applied. Then, the displacement of the piezoelectric film 142 applies the driving voltage PD1. It increases the size of the ink droplets that are larger than ever before and discharges, that is, by increasing the displacement of the piezoelectric film 142 to compensate for the size of the ink droplets reduced by the retreat of the meniscus. The size of the droplets can be made approximately the same as the size of the first ejected ink droplets After the second ink droplet is ejected, the meniscus retreats a further back from the tip of the nozzle 122 as shown in Fig. 1C. It is. duration d ₃ ((e.g. 6㎲) of the driving pulse (P3) by the application to compensate for ink drop size enemy reduced by retraction of the meniscus to discharge an ink drop also three times with the same size Can be.

As a third embodiment of the driving method according to the present invention, as shown in Figure 7, the initial driving voltage (V ₄ , V ₅ , V ₆ ) and the driving time (PVD1, PVD2, PVD3) in which the durations d ₄ , d ₅ , and d ₆ all change may be considered. At this time, the driving voltage V ₄ , ₄ to be V ₄ d ₄ <V ₅ d ₅ <V ₆ d ₆ V ₅ , By adjusting V ₆ ) and the durations d ₄ , d ₅ , d ₆ , the same effects as in the above-described first and second embodiments can be obtained.

By such a driving method, ink droplets of the same size can be discharged even at the beginning of printing. The number of driving voltages and / or delay times to which the driving pulses may vary depends on the viscosity of the ink, the frequency of the driving pulses, and the structure of the printhead. By changing the delay time, the meniscus's position is almost stable.

When the driving pulse is continuously applied to the piezoelectric actuator 140, the size of the ink droplets continues to decrease, and when the flow of the ink in the ink flow passage reaches a steady state, the position of the meniscus is fixed. The enemy is discharged continuously. Therefore, when the position of the meniscus is stabilized by the driving pulses as shown in FIGS. 3, 5, and 7, it is possible to continuously discharge a certain size of ink droplets by continuously applying a constant driving pulse. . At this time, the last driving pulses PV3, PD3, PVD3 can be continuously applied.

As described above, according to the driving method of the piezoelectric inkjet printhead according to the present invention, the following effects can be obtained.

In the past, it was difficult to realize high quality at high speed because ink droplets were uneven in the initial printing stage. In particular, when applied to the manufacturing process of the color filter of the liquid crystal display device, the manufacturing process of the light emitting layer of the organic light emitting diode (OLED), the manufacturing process of the organic thin film transistor (OTFT), etc., the thickness of the thin film formed by the discharged ink is uneven. There was a problem of getting lost. However, if the driving method according to the present invention is applied, ink droplets of a predetermined size can be discharged from the beginning of printing. Therefore, high speed and high quality printing is possible. In addition, when applied to industrial processes, such as the manufacturing process of the color filter of a liquid crystal display device using a high viscosity ink, the manufacturing process of the light emitting layer of an organic light emitting diode (OLED), and the manufacturing process of an organic thin film transistor (OTFT), uniform thickness is carried out. It can form a thin film, and can improve the speed of the manufacturing process.

In the past, the ink was consumed by discharging the ink several times until the ink droplet was stabilized and then printing. However, according to the driving method of the present invention, ink droplets having the same size can be discharged even at the beginning of printing. It is possible to improve the ink utilization rate.

While the preferred embodiments of the present invention have been described in detail, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

Claims (6)

A method of driving a piezoelectric inkjet printhead in which a discharge pressure is generated by changing a volume of a pressure chamber using a piezoelectric actuator to eject ink through a nozzle.  At the beginning of printing, an initial driving pulse in which at least one of a driving voltage and a duration thereof is changed until the position of the meniscus in the nozzle is stabilized is applied to the piezoelectric actuator so that the volume of ink droplets discharged is constant. And a piezoelectric inkjet printhead. The method of claim 1, A method of driving a piezoelectric inkjet printhead, wherein the duration of the initial driving pulse is fixed and the driving voltage is gradually increased. The method of claim 1, A method of driving a piezoelectric inkjet printhead, wherein the driving voltage of the initial driving pulse is fixed and a duration is gradually increased. The method of claim 1, And gradually increasing the product of the driving voltage and the delay time of the initial driving pulse. The method according to any one of claims 1 to 4, The number of the initial drive pulses is less than 10 drive method of the piezoelectric inkjet printhead. The method according to any one of claims 1 to 4, And after the position of the meniscus in the nozzle is stabilized, a driving pulse having a last driving voltage and a duration is applied to the piezoelectric actuator.

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