JP2006088392A - Inkjet recording head and inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve ink drop discharge efficiency by means of a simple structure while restraining a drop in a refilling speed. <P>SOLUTION: An electrode plate 38 is arranged on the under side of a pressure chamber plate 32 and the upper side of a through plate 28 of a part forming an ink supply route 18. When voltage is applied to the electrode plate 38, an electric field occurs in the ink supply route 18 and ink viscosity increases. When the application of voltage to the electrode plate 38 is stopped, an electric field in the ink supply route 18 disappears and ink viscosity lowers to an ordinary level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus that performs image recording by ejecting ink droplets, and an ink jet recording head applied to the ink jet recording apparatus.

  Some ink jet recording apparatuses eject ink droplets by generating a pressure wave with respect to ink filled in a pressure chamber of an ink jet recording head by bending deformation of a so-called piezoelectric actuator. In this ink jet recording apparatus, the operation of ejecting ink droplets is generally performed as follows. First, the piezoelectric actuator is driven to generate a pressure wave in the ink in the pressure chamber, and ink droplets are ejected from the ink ejection nozzle. After the ink droplet is ejected, the ink is drawn (refilled) from the pool chamber in which ink is stored to the pressure chamber side by the surface tension of the meniscus to prepare for the next ink droplet ejection.

  By the way, the pressure wave generated in the ink in the pressure chamber at the time of ink droplet ejection includes a component that travels from the pressure chamber toward the ink ejection nozzle (a component effective for ink droplet ejection) and a pool through the ink supply path. There are components that leak into the chamber. The leakage of the pressure wave has a disadvantage that the ink droplet ejection efficiency is lowered.

  In order to prevent this drop in ink droplet ejection efficiency, the length of the supply path for supplying ink from the pool chamber to the pressure chamber is increased or the diameter of the supply path is reduced. Such a technique is disclosed (see Patent Document 1). However, the technique described in Patent Document 1 can suppress the progression component (leakage) of the pressure wave to the pool chamber side, but the refill speed also becomes slow, and it takes a long time to discharge the next ink droplet. There has been a problem that the frequency of discharge becomes low.

In addition, a technique is also disclosed in which a mechanical movable valve is disposed in a supply path for supplying ink from the pool chamber to the pressure chamber in order to suppress the progression component (leakage) of the pressure wave to the pool chamber side (see FIG. Patent Document 2). However, when the movable valve is provided, the manufacturing process becomes complicated, and further, it is difficult to increase the mechanical reliability of the movable valve.
JP 2003-211659 A JP-A-6-198872

  The present invention has been made in consideration of the above facts, and is to obtain an ink jet recording head having a simple configuration and capable of improving ink droplet ejection efficiency while suppressing a decrease in refill speed. Objective.

  In order to achieve the above object, an ink jet recording head according to claim 1 includes a pool chamber that stores ink, an ink discharge nozzle that discharges ink droplets, an ink filled and the ink discharge nozzle, A pressure chamber that communicates with the pool chamber and generates a pressure wave for ejecting ink droplets from the ink ejection nozzle; and formed between the pool chamber and the pressure chamber; Ink supply path for supplying ink and the viscosity of the ink in the ink supply path at the time of ink droplet ejection, and lowering the viscosity of the ink in the ink supply path at the time of refill after ink droplet ejection than at the time of ink ejection And a viscosity control means.

  In the ink jet recording head of the present invention, the pressure chamber communicates with the ink discharge nozzle and the pool chamber. An ink supply path is formed between the pressure chamber and the pool chamber, and ink stored in the pool chamber is supplied to the pressure chamber via the ink supply path. The viscosity of the ink in the ink supply path is controlled by the viscosity control means so that the viscosity increases when the ink droplet is discharged, and so that the viscosity is lower than when the ink is discharged when refilling after the ink droplet is discharged. Here, the refill is an operation for drawing ink from the pool chamber to the pressure chamber side after ink droplet ejection to prepare for the next ink droplet ejection.

  According to the above configuration, when ink droplets are ejected, the pressure wave generated in the pressure chamber is less likely to travel to the pool chamber due to an increase in ink viscosity in the ink supply path, and ink droplet ejection efficiency can be improved. . Further, at the time of refilling after ink droplet ejection, the ink is likely to pass from the pool chamber to the pressure chamber due to a decrease in ink viscosity in the ink supply path, and a decrease in refilling speed can be prevented. Furthermore, a simple configuration for controlling the viscosity of the ink can be achieved without requiring a mechanical operation.

  In the ink jet recording head of the present invention, as described in claim 2, the ink is an ER fluid whose viscosity is increased by applying an electric field, and the viscosity control means is disposed on both sides of the ink supply path. And an electrode capable of generating an electric field in the ink supply path by applying a voltage and eliminating the electric field generated in the ink supply path by stopping the voltage application.

  The ER (Electro Rheological) fluid is a fluid having a property of increasing viscosity (behaves like a viscosity) by applying an electric field. In the above configuration, the electrodes are provided on both sides of the ink supply path. By applying a voltage to this electrode to generate an electric field in the ink supply path, the viscosity of the ink in the ink supply path can be increased. Further, by applying no voltage to the electrode and making no electric field in the ink supply path, the viscosity of the ink in the raised ink supply path can be lowered (returned to the original viscosity) as compared with the time of ink ejection. it can.

  According to the above configuration, the viscosity of the ink can be controlled by a simple configuration in which electrodes are disposed and a simple operation of applying a voltage, compared with a case where a movable valve requiring mechanical operation is used. Thus, it is possible to easily prevent a drop in ink droplet ejection efficiency.

  In the ink jet recording head of the present invention, as described in claim 3, the ink is an MR fluid whose viscosity increases by applying a magnetic field, and the viscosity control means is located in the vicinity of the ink supply path. It is also possible to include a magnetic field generating device that is provided and can generate a magnetic field in the ink supply path by applying a magnetic field, and cancel the magnetic field generated in the ink supply path by stopping the magnetic field application.

  An MR (Magneto Rheological) fluid is a fluid having the property of increasing viscosity (behaves like a viscosity) by applying a magnetic field. In the above configuration, the magnetic field generating device is provided in the vicinity of the ink supply path. By applying a magnetic field to the magnetic field generation device to generate a magnetic field in the ink supply path, the viscosity of the ink in the ink supply path can be increased. In addition, by applying no magnetic field to the magnetic field generation device and making the ink supply path have no magnetic field, the viscosity of the ink in the raised ink supply path can be reduced.

  According to the above configuration, the viscosity of the ink can be controlled with a simple configuration in which a magnetic field generating device is disposed and a simple operation of applying a magnetic field, compared with the case of using a movable valve that requires mechanical operation. Thus, it is possible to easily prevent a drop in ink droplet ejection efficiency.

  In addition, the said magnetic field generation device can be comprised with an electromagnet as described in Claim 4.

  Further, according to the ink jet recording head of the present invention, as described in claim 5, the viscosity control means is in a state in which the viscosity of the ink in the ink supply path is increased except during refilling after ink droplet ejection. It can also be characterized by holding.

  When ink droplets are ejected from an adjacent ink ejection nozzle, the ink filled in the pressure chamber is transmitted with vibration, the meniscus vibrates, and the size of the ejected ink droplet changes depending on the meniscus position. It may end up. Therefore, as described above, the viscosity of the ink in the ink supply path is maintained in an increased state except during refilling after ink droplet ejection. This makes it difficult for vibration from the adjacent ink discharge nozzles to be transmitted, suppresses vibration of the meniscus, and makes it possible to make the size of the ejected ink droplets constant.

  According to a sixth aspect of the present invention, in the ink jet recording head according to the sixth aspect, the viscosity control means controls the viscosity so as to erase the residual pressure wave in the pressure chamber after ink droplet ejection. You can also.

  If the pressure wave generated in the pressure chamber remains after the ink droplet is ejected, the meniscus may be vibrated by the influence, and the size of the ejected ink droplet may change depending on the meniscus position. Therefore, as described above, the viscosity control means performs viscosity control so as to erase the residual pressure wave in the pressure chamber after ink droplet ejection. Thereby, the residual pressure wave in the pressure chamber is eliminated, and the meniscus position can be maintained at a predetermined position.

  An ink jet recording apparatus according to a sixth aspect includes the ink jet recording head according to any one of the first to fifth aspects.

  According to the present invention, when ink droplets are ejected, the pressure wave generated in the pressure chamber is less likely to travel to the pool chamber due to an increase in ink viscosity in the ink supply path, and ink droplet ejection efficiency can be improved. . Further, at the time of refilling after ink droplet ejection, the ink is likely to pass from the pool chamber to the pressure chamber due to a decrease in ink viscosity in the ink supply path, and a decrease in refilling speed can be prevented. ,

  As described above, according to the present invention, ink droplet ejection efficiency can be improved with a simple configuration and while suppressing a decrease in refill speed.

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

  As shown in FIG. 1, the ink jet recording apparatus 102 includes a carriage 104 on which an ink jet recording head 112 is mounted, and moves the carriage 104 in a predetermined main scanning direction along the recording surface of the recording paper P (main scanning). The main scanning mechanism 106 and the sub-scanning mechanism 108 for conveying (sub-scanning) the recording paper P in a predetermined sub-scanning direction that intersects (preferably orthogonally) the main scanning direction are configured. In the drawings, the main scanning direction is indicated by an arrow M, and the sub-scanning direction is indicated by an arrow S.

  The ink jet recording head 112 is mounted on the carriage 104 so that the nozzle surface (see FIGS. 1 and 2) on which the ink discharge nozzles 10 are formed faces the recording paper P, and the main scanning mechanism 106 performs the main scanning direction. By ejecting ink droplets onto the recording paper P while being moved, the image is recorded on a certain band region BE. When one movement in the main scanning direction is completed, the recording paper P is conveyed in the sub scanning direction by the sub scanning mechanism 108, and the next band area is recorded while moving the carriage 104 in the main scanning direction again. By repeating such an operation a plurality of times, image recording can be performed over the entire surface of the recording paper P.

  As shown in FIGS. 2 and 3, the inkjet recording head 112 includes the nozzle plate 22, the ink pool plates 24 and 26, the through plate 28, the ink supply path plate 30, the pressure chamber plate 32, and the vibration plate 34 in order. It is formed by stacking. The ink ejection nozzle 10 is formed on the nozzle plate 22, and the nozzle communication chamber 16 and the pool chamber 14 are formed on the ink pool plates 24 and 26. The nozzle communication chamber 16 is configured above the ink discharge nozzle 10 and communicates with a pressure chamber 12 described later. The upper wall of the pool chamber 14 is a through plate 28, and the lower wall is a nozzle plate 22. In the through plate 28, the nozzle communication chamber 16 and the opening 20 are formed. The opening 20 is disposed in the upper part of the pool chamber 14. A pressure chamber 12 is formed in the pressure chamber plate 32. The upper wall of the pressure chamber 12 is constituted by a vibration plate 34, and the lower wall is constituted by an ink supply path plate 30. An ink supply path 18 that connects the pressure chamber 12 and the pool chamber 14 is formed in the ink supply path plate 30. The upper wall of the ink supply path 18 is constituted by a pressure chamber plate 32, and the lower wall is constituted by a through plate 28. The ink stored in the pool chamber 14 is supplied to the pressure chamber 12 through the ink supply path 18.

  An electrode plate 38 is disposed below the pressure chamber plate 32 and above the through plate 28 in the portion constituting the ink supply path 18. As shown in FIG. 4, the electrode plate 38 is connected to the drive circuit 40, and voltage application is turned on and off.

  A diaphragm 34 is disposed on the upper surface of the pressure chamber 12, and a piezoelectric element 36 is disposed on the upper surface of the diaphragm 34. As shown in FIG. 4, the piezoelectric element 36 is connected to the drive circuit 40 and is driven according to the drive pulse applied from the drive circuit 40.

  An operation when ink droplets are ejected from the inkjet recording head 112 having the above-described configuration will be described.

  As shown in FIG. 7, when an instruction signal for ejecting ink droplets is input to the drive circuit 40, voltage is first applied from the drive circuit 40 to the electrode plate 38 (1). As a result, an electric field is generated in the ink supply path 18, and the ink particles that have been dispersed as shown in FIG. 5A are connected as shown in FIG. 5B to form a chain structure. The viscosity of the ink in the ink supply path 18 increases.

  Next, a drive pulse is applied from the drive circuit 40 to the piezoelectric element 36 (2), and the piezoelectric element 36 is driven. As a result, a pressure wave P is generated in the pressure chamber 12. Since the ink viscosity in the ink supply path 18 is high, as shown in FIG. 6A, the pressure wave P hardly leaks to the pool chamber 14 side. On the other hand, since there is no leakage to the pool chamber 14 side to the ink discharge nozzle 10 side, the pressure wave P is efficiently transmitted, and ink droplets are discharged from the ink discharge nozzle 10.

  After ejection of the ink droplet, voltage application from the drive circuit 40 to the electrode plate 38 is stopped (3). As a result, the electric field generated in the ink supply path 18 is eliminated, and the ink particles constituting the chain structure as shown in FIG. 5B are discrete as shown in FIG. As a result, the ink viscosity in the ink supply path 18 decreases. For this reason, at the time of refilling after ink droplet ejection, ink easily passes from the pool chamber 14 to the pressure chamber 12 through the ink supply path 18 (see FIG. 6B), and a decrease in refilling speed is prevented. Can do.

  After the refill is completed, the voltage may be applied again from the drive circuit 40 to the electrode plate 38 (4), or the voltage application may be stopped until the next ink droplet ejection. That is, as shown in (A) of the timing chart of FIG. 7, a voltage is constantly applied to the electrode plate 38 to maintain the ink viscosity in the ink supply path 18 at a high level except during refilling during printing. As shown in FIG. 7B, a voltage is applied to the electrode plate 38 only when ink droplets are being ejected during printing to increase the viscosity of the ink in the ink supply path 18, and otherwise. In this case, voltage may not be applied to the electrode plate 38, and the viscosity of the ink in the ink supply path 18 may be set to a normal viscosity.

  In particular, as shown in FIG. 7A, by constantly applying a voltage to the electrode plate 38 and maintaining the viscosity of the ink in the ink supply path 18 at a high level except during refilling during printing execution, The following effects are obtained. Normally, when an ink droplet is ejected from the adjacent ink ejection nozzle 10, a pressure wave is transmitted through the pool chamber 14. Due to this pressure wave, the meniscus of the ink discharge nozzle 10 vibrates and the position of the meniscus is displaced, so that the droplet volume of the ink droplet to be discharged next changes. Therefore, the viscosity in the ink supply path 18 is increased to make it difficult for pressure waves to be transmitted from the pool chamber 14. Thereby, the vibration of the meniscus is suppressed, and the droplet volume of the ejected ink droplet can be made constant.

  Further, as shown in FIG. 7C, after discharging the ink droplets, the time for stopping the voltage application may be slightly delayed to cancel the residual pressure wave.

  In FIG. 8, in the inkjet recording head 112 having the above-described configuration, the structure of the ink supply path 18 is the same, and the viscosity of the ink in the ink supply path 18 is controlled and the control of the ink viscosity is not performed (the voltage is changed). The result of comparing the drop volume and refill time of the ink drop is shown. When no ink is applied to the ink supply path 18 and ink droplets are ejected and refilled with the ink viscosity in a normal state (no viscosity control), the ink droplet droplet volume and refill time are set to 1. When ink droplets were ejected after applying a voltage to the supply path 18 to increase the ink viscosity (with viscosity control), the droplet volume of the ink droplets increased to 1.3. Further, when the application of voltage was stopped at the time of refilling to reduce the ink viscosity (with viscosity control), the refill time was 1 and was the same as the case without viscosity control. That is, it can be seen that by controlling the ink viscosity as in the above embodiment, the ink droplet ejection efficiency can be improved while maintaining the refill speed.

  In FIG. 9, in the ink jet recording head 112 configured as described above, the ink supply path 18 has a conventional structure and the ink viscosity is not controlled, and the ink supply path 18 has a structure that is looser than the conventional structure. The results of comparing the drop volume and refill time of the ink droplets when the resistance is decreased (increase in cross-sectional area, length is increased) and the viscosity of the ink in the ink supply path 18 is controlled are shown. ing. When no ink is applied to the ink supply path 18 and ink droplets are ejected and refilled with the ink viscosity in a normal state (no viscosity control), the ink droplet droplet volume and refill time are set to 1. When ink droplets were ejected after applying a voltage to the supply path 18 to increase the ink viscosity (with viscosity control), the droplet volume of the ink droplets was 1 and the viscosity was not controlled. . In addition, when the application of voltage is stopped at the time of refilling to reduce the ink viscosity (with viscosity control), the refill time is 0.6, which is shorter than the case without viscosity control. That is, it can be seen that by controlling the ink viscosity as in the above embodiment, the ink discharge efficiency can be maintained and the refill speed can be shortened even if the fluid resistance of the ink supply is reduced to 18.

  In FIG. 10, when ink droplets are ejected from one ink ejection nozzle 10, the meniscus vibration amplitude of adjacent ink ejection nozzles 10 is compared with and without ink viscosity control. Results are shown. When ink viscosity control was not performed, that is, when the ink viscosity was kept in a normal state, the vibration amplitude of the meniscus was 20 μm. On the other hand, when the ink viscosity in the ink supply path 18 is controlled, that is, when the ink viscosity is increased by applying a voltage to the ink supply path 18, the vibration amplitude of the meniscus is 5 μm. Since the droplet volume of the ejected ink droplet changes depending on the position of the meniscus, the smaller the meniscus vibration amplitude, the more stable the droplet volume. From the above results, it can be seen that the meniscus vibration due to the influence of the pressure wave from the adjacent ejector can be suppressed by increasing the ink viscosity in the ink supply path 18 except during the refilling operation.

  As described above, according to the present embodiment, the ink viscosity is controlled so that the ink viscosity in the ink supply path 18 is increased during ink droplet ejection and the ink viscosity in the ink supply path 18 is decreased during refilling. Ink ejection efficiency can be improved without reducing the refill speed. Further, since the ink viscosity is controlled by applying a voltage to the electrode plate 38, the control can be easily performed as compared with the case where a movable valve with a mechanical operation is used.

  In the above-described embodiment, an example in which ER fluid is used as the ink has been described. However, MR (Magneto Rheological) fluid can also be used as ink. MR fluid has a high viscosity by applying a magnetic field. In this case, instead of the electrode plate 38, an electromagnet is arranged in the vicinity of the ink supply path 18, and a magnetic field is applied to the electromagnet. Then, a magnetic field is generated in the ink supply path 18, thereby increasing the viscosity of the ink that is the MR fluid, and by stopping the application of the magnetic field, the viscosity of the ink is reduced to the normal level. The above-described effects can be obtained by controlling the ink viscosity in the same manner as in the case of the ER fluid.

  Further, an ink having a property that its viscosity changes with temperature change can also be used. In this case, a heater is disposed in the ink supply path 18 instead of the electrode plate 38, and the ink viscosity is controlled by changing the temperature by turning the heater on and off.

It is a schematic perspective view which shows an inkjet recording device. (A) is a figure which shows the principal part of an inkjet recording head. (B) is the enlarged view of the X section of (A). It is sectional drawing which shows the structure of a part of inkjet recording head. It is a schematic block diagram of the drive system of an inkjet recording head. (A) is explanatory drawing which shows the state of the ink particle when voltage is not applied, (B) is explanatory drawing which shows the state of the ink particle when voltage is applied. (A) of the ink in an inkjet recording head is a figure which shows the state in which the piezoelectric element was driven and the pressure wave has generate | occur | produced, (B) is a figure which shows the state at the time of refill. It is a chart which shows the timing of the voltage application to the ink droplet discharge signal during printing operation, the drive pulse to a piezoelectric element, and an electrode plate. FIG. 6 is a graph comparing ink droplet volume and refill speed when the ink viscosity is controlled and when the ink viscosity is not controlled when the ink supply paths have the same configuration. FIG. 5 is a graph comparing the ink droplet volume and the refill speed when the ink viscosity is not controlled and when the ink resistance in the ink supply path is reduced and the ink viscosity is controlled. 6 is a graph comparing meniscus vibration amplitudes in an ink supply path between a normal ink viscosity and a high ink viscosity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ink discharge nozzle 12 Pressure chamber 14 Pool chamber 16 Nozzle communication chamber 18 Ink supply path 22 Nozzle plate 24 Ink pool plate 28 Through plate 30 Ink supply path plate 32 Pressure chamber plate 34 Vibration plate 36 Piezoelectric element 38 Electrode plate 40 Drive circuit 102 Inkjet recording device 112 Inkjet recording head P Pressure wave

Claims (7)

A pool room for storing ink;
An ink discharge nozzle for discharging ink droplets;
A pressure chamber that is filled with ink and communicates with the ink discharge nozzle and the pool chamber to generate a pressure wave for discharging an ink droplet from the ink discharge nozzle;
An ink supply path that is formed between the pool chamber and the pressure chamber and supplies ink from the pool chamber to the pressure chamber;
Viscosity control means for increasing the viscosity of the ink in the ink supply path at the time of ink droplet discharge, and lowering the viscosity of the ink in the ink supply path at the time of refill after ink droplet discharge;
An ink jet recording head comprising: The ink is an ER fluid whose viscosity increases by applying an electric field,
The viscosity control means is provided on both sides of the ink supply path, generates an electric field to the ink supply path by applying a voltage, and cancels the electric field generated in the ink supply path by stopping the voltage application. The inkjet recording head according to claim 1, wherein the inkjet recording head is configured to include a possible electrode. The ink is an MR fluid whose viscosity increases by applying a magnetic field,
The viscosity control means is provided in the vicinity of the ink supply path, can generate a magnetic field to the ink supply path by applying a magnetic field, and can cancel the magnetic field generated in the ink supply path by stopping the magnetic field application. The inkjet recording head according to claim 1, comprising a magnetic field generating device.   The inkjet recording head according to claim 3, wherein the magnetic field generating device is an electromagnet.   5. The viscosity control unit according to claim 1, wherein the viscosity control unit holds the ink in the ink supply path in an increased state except during refilling after ink droplet ejection. 2. An ink jet recording head according to 1.   5. The ink jet recording head according to claim 1, wherein the viscosity control unit performs viscosity control so as to erase a residual pressure wave in the pressure chamber after ink droplet ejection.   An ink jet recording apparatus comprising the ink jet recording head according to claim 1.

Images