JPH091833A - Ink jet recorder - Google Patents

Abstract

PURPOSE: To concentrate a high frequency oscillation energy generated by each piezoelectric member substantially to the center of the area sandwiched by the members, and to efficiently atomize ink to inject the ink. CONSTITUTION: The ink jet recorder comprises boards 21 oppositely disposed and a nozzle plate 26 having nozzle holes 26a, and an ink chamber 27 is formed therebetween. Two or more piezoelectric members 30, 31 per one ink chamber are so disposed as to be opposed to each other on the board 21 of the chamber 27. High frequency pulse voltages having the frequency of the natural oscillation frequency or more are synchronously applied to the members 30, 31 in response to an image signal by a controller of voltage applying means, the ink charged in the chamber 27 is atomized and injected from the hole 26a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for ejecting an ink mist according to an image signal and recording it on a recording medium.

[0002]

2. Description of the Related Art Conventionally, a high frequency vibration generating means such as a piezoelectric material is used to mist the ink, and the ink mist is selectively ejected from a nozzle in accordance with an image signal to form an image on a recording medium such as paper. Various proposals have been made regarding the technology. As an example thereof, in the ink jet head disclosed in Japanese Patent Laid-Open No. 5-57891, electrodes are formed on the front and back surfaces of a flat piezoelectric substrate, and a voltage that fluctuates at a cycle equal to the resonance frequency is applied to these electrodes. By virtue of this, the piezoelectric substrate is locally vibrated at high frequency, and at the same time, the nozzle plate arranged opposite to the piezoelectric substrate is also vibrated at high frequency, and the ink filled in the ink chamber is misted by the interference of these vibrations so that the nozzles I am trying to jet more.

[0003]

However, in the above-mentioned conventional ink jet head, the piezoelectric material, which is the oscillation source for exciting the ink at a high frequency, has a flat shape, so that the ink mist can be efficiently generated. Have difficulty.

[0004]

Therefore, an ink jet recording apparatus of the present invention has been made to solve the above-mentioned problems, and an ink chamber formed between a substrate and a nozzle plate having nozzles, and the above ink. Two or more piezoelectric members arranged so as to face each other on the substrate of the chamber, and a high-frequency pulse voltage having a frequency equal to or higher than the natural frequency of the piezoelectric member according to an image signal is synchronized with each piezoelectric member. A voltage applying unit for applying a voltage is applied to the piezoelectric member by the voltage applying unit to vibrate at a high frequency, and the ink filled in the ink chamber is misted and ejected from the nozzle.

In the above ink jet recording apparatus, it is preferable that the nozzle is sandwiched between the piezoelectric members or formed at a position of the nozzle plate corresponding to substantially the center of the enclosed area.

[0006]

According to the ink jet recording apparatus, when the high voltage pulse voltage having a frequency higher than its natural frequency is synchronously applied to each piezoelectric member by the voltage applying means, each piezoelectric member is deformed and restored at high speed. Repeatedly vibrates at high frequency. Since the piezoelectric members are arranged on the substrate of the ink chamber so as to face each other, the high frequency vibration energy generated by the vibration of the piezoelectric member propagates through the ink filled in the ink chamber and is sandwiched between the piezoelectric members. After being concentrated or concentrated in the substantially central portion of the enclosed area, it is transmitted to the ink meniscus held by the surface tension in the nozzle and vibrates the surface violently to make the ink mist and fly. Also, cavitation occurs near the surface of the piezoelectric member that vibrates at high frequency,
The interference of shock waves due to this cavitation also promotes the formation of mist in the ink.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows the overall configuration of an inkjet recording device 1 according to the present invention.
The inkjet recording apparatus 1 is roughly classified into a connector 2
a, a power supply unit 2, a drive system 3, a mechanical controller 4, a memory 5, a controller 6, and an ink supply unit 7.
, Scan carriage 8, paper feed unit 9, and case 10
And an operation panel 11. The scan carriage 8 is capable of scanning in a direction orthogonal to the paper passing direction (direction of arrow a) (front and back direction of the paper surface in FIG. 1), and inside the carriage 4 is provided for each color of black, cyan, magenta and yellow. Two inkjet heads 12
Are arranged along the paper passing direction and the ink jet nozzles are directed downward.

The ink jet head 12 has a bottom plate 20, as shown in FIG. A substrate 21 made of a high-rigidity non-piezoelectric material such as alumina is provided above the bottom plate 20, and spacers 22 and 2 are provided on both sides of the substrate 21.
3 and 3 are fixed. The substrate 21 and the spacer 2
Side walls 24 and 25 are fixed to the upper portions of 2, 23 at predetermined intervals. Also, these side walls 24,
A nozzle plate 26 having a nozzle hole 26 a is fixed to the upper part of the wall 25 between the substrate 21 and the nozzle plate 26 which are arranged to face each other, and the side wall 2
An ink chamber 27 is formed in a space area sandwiched between 4, 25. In order to supply ink to the ink chamber 27,
An ink supply path 28 is formed below the side wall 25.

On the substrate 21 of the ink chamber 27, two piezoelectric members 30 and 31 per one ink chamber 27 are arranged in a tuning fork shape so as to face each other at a predetermined interval. The piezoelectric members 30 and 31 are each formed of a rectangular parallelepiped made of PZT, for example. The nozzle hole 26a of the nozzle plate 26 is formed so as to be wide inside the ink chamber 27 and narrow outside thereof at a position corresponding to the central portion 32 of the region sandwiched by the piezoelectric members 30 and 31. It

As shown in FIG. 3, the piezoelectric members 30 and 31 are fixed to the substrate 21 via insulating adhesive layers 33 and 34, respectively. In addition, on both side surfaces of the piezoelectric members 30 and 31, an Au / Ni film formed by a plating method or an Au / (Ni, Cr) film formed by sputtering and having a thickness of about 0.1 to 10 μm is formed. Has been formed.
First formed on the facing surfaces of the piezoelectric members 30 and 31, respectively.
The electrodes 35 and 36 are connected to the conductive adhesive layer 37 formed on the upper surface of the substrate 21 continuously with the arranged plurality of ink chambers 27, and are formed on the side opposite to the first electrodes 35 and 36. The two electrodes 38, 39 are provided on the upper surface of the substrate 21 for each ink chamber 2.
7 are connected to the conductive adhesive layers 40 and 41 formed respectively. Furthermore, as shown by the arrow in FIG.
Both the piezoelectric members 30 and 31 are polarized in the direction opposite to the substrate 21.

When the ink chamber 27 is filled with ink, the piezoelectric members 30 and 31 come into direct contact with the ink.
On the surface of the substrate 21, for example, a polyimide resin is applied by a spin coating method and baked at 180 ° C. for 1 hour to form the overcoat film 42. This is to prevent the ink from penetrating into the piezoelectric members 30 and 31 to reduce the resistance, thereby preventing the effective voltage from being applied and reducing the vibration efficiency.

As will be described later, when the ink is misted, a pulse voltage is applied to the piezoelectric members 30 and 31 to vibrate at a high frequency. To stabilize the mist formation, as shown in FIG. It is preferable to set the width w of each of the piezoelectric members 30 and 31 to be less than or equal to the height h thereof. Further, as shown in FIG. 5, a groove 29 is formed on the substrate 21 between the piezoelectric members 30 and 31, and the depth d from the upper surface of the piezoelectric member to the bottom surface of the groove 29 is higher than that of the piezoelectric members 30 and 31. If the volume of the region sandwiched by the piezoelectric members is increased so as to be equal to or greater than h, more stable mist formation of ink can be achieved.

In this embodiment, two piezoelectric members 30 and 31 are bonded and fixed on the substrate 21 to form a tuning fork-shaped oscillation source. However, the shape shown in FIG. 4 or 5 is integrally formed by a piezoelectric material. You may form in. By doing so, the piezoelectric member 3
Processes such as bonding of 0 and 31 and processing of the groove 29 can be omitted, which facilitates manufacturing.

FIG. 6 shows the ink jet head 12 of FIG.
4 is a sectional view taken along line IV-IV in FIG. A plurality of the ink chambers 27 are formed by being partitioned by a plurality of partition walls 44, and a plurality of the nozzle holes 26a are also formed corresponding to each ink chamber 27, and the formation pitch thereof is 42.3 to 254 μm ( Pixel density: 600-100dp
i) about the same.

An ink manifold 45 is attached to the side surface of the ink jet head 12 as shown in FIG. A common ink chamber that communicates with all of the ink supply passages 28 formed in each ink chamber 27 is formed therein, and ink is supplied from the direction of arrow b.

The ink jet head 12 is fixed on a head base 47. On the head base 47, one lead wire 48 connected to the ground is formed at one end side in the arrangement direction of each nozzle hole 26a, and the lead wire 48 is continuous with each ink chamber 27. Conductive adhesive layer 37 on the substrate 21 formed by
, And the piezoelectric members 3 arranged in all the ink chambers 27 by connecting them by wire bonding 49 or the like.
The 0, 31 first electrodes 35, 36 are grounded. on the other hand,
The lead wiring 5 is provided on both ends of the head base 47 in the direction orthogonal to the arrangement direction of the nozzle holes 26a.
0 and 51 are formed corresponding to the respective ink chambers 27. These lead wires 50 and 51 are connected to a controller 6 (see FIG. 1) which is a voltage applying means via a driver IC (not shown), and inside the head, the second electrodes 38 of the piezoelectric members 30 and 31 are connected. Three
9 are respectively connected to the conductive adhesive layers 40 and 41 which are electrically connected. As a result, the piezoelectric members 30 and 31 have
A voltage is applied by the controller 6 according to the image signal.

Next, the ink mist ejecting operation of the ink jet head 12 having the above structure will be described.
Ink is filled in each ink chamber 27 from the ink supply unit 7 (see FIG. 1) via the ink manifold 45 and the ink supply passage 28. A positive pulse voltage as shown in FIG. 8A is applied by the controller 6 to the piezoelectric members 30 and 31 arranged in the ink chamber 27. This pulse voltage represents one image signal for forming one pixel dot on the recording paper, and a plurality of original pulses 52 having a frequency f higher than the natural frequency of the piezoelectric members 30 and 31.
Are assembled and configured. The original pulse 52 is shown in FIG.
It is preferable to form a rectangular shape as shown in FIG. 1 and its frequency f is within a range of 20 kHz (kilohertz) to 200 MHz (megahertz). Further, within the above range, 40 kHz to 1
The range of 00 MHz is particularly preferable because the influence of various fluctuation factors such as temperature dependence, long-term use, first mist ejection after suspension, and the like can be reduced, and ink mist formation can be performed more stably.

When the pulse voltage shown in FIG. 8A is applied, inside the piezoelectric members 30 and 31, as shown in FIG. 9, the second electrodes 38 and 39 are changed to the first electrodes 35 and 36. An electric field is formed in each direction, that is, in the direction orthogonal to the polarization direction. Thereby, the piezoelectric members 30, 31
Vibrates at high frequency by repeating deformation based on a so-called sliding vibration mode (share mode) at high speed.

Specifically, when the original pulse 52 constituting the pulse voltage is turned on, as shown by the broken line in FIG. 9, the upper portions of the piezoelectric members 30 and 31 arranged in a tuning fork shape are momentarily moved in a direction approaching each other. When the original pulse 52 is off, the original pulse 52 is restored based on its elasticity. This deformation is repeated at a high speed according to the number of the original pulses 52 included in one image signal to vibrate at high frequency. This vibration generates high-frequency vibration energy that vibrates the ink in the area sandwiched between the piezoelectric members 30 and 31. Since the piezoelectric members 30 and 31 are arranged to face each other and vibrate in synchronization with each other, the high-frequency vibration energy is concentrated in the substantially central portion 32 of the region sandwiched between them. As shown in FIG. 10, the concentrated high-frequency vibration energy propagates through the ink and is transmitted to the ink meniscus held by the surface tension in the nozzle hole 26a, vibrating the surface 53 vigorously, and ejects the ink as a mist. . Further, cavitation is generated near the surfaces of the piezoelectric members 30 and 31 that vibrate at high frequency, and the mist of the ink is promoted by the interference of the shock wave due to the cavitation.

The ink mist ejected in a direction substantially perpendicular to the nozzle plate 26 adheres to recording paper (not shown). On the other hand, the ink chamber 27 in which the ink amount has slightly decreased by the mist ejection is replenished with ink by the capillary phenomenon via the ink supply passage 28. Such an ink mist ejecting operation is independently performed for each ink chamber 27 according to an image signal, and an image corresponding to the number of nozzles is drawn by the scan movement of the scan carriage 8, which is the sheet passing direction. The image is formed on the recording paper by being repeated in synchronization with the movement to.

As described above, according to this embodiment, the two piezoelectric members 30 and 31 which are the oscillation sources are arranged so as to face each other like a tuning fork, and are vibrated in synchronization with each other. Energy is transferred to each piezoelectric member 30, 3
The ink can be concentrated in the substantially central portion 32 of the region sandwiched by 1, and the ink can be efficiently misted with a small amount of energy. Further, the nozzle hole 26a is formed in the central portion 32.
Since it is formed at the position of the nozzle plate 26 corresponding to, it can be used for mist formation of ink without loss of concentrated high frequency vibration energy, and more efficient mist ejection becomes possible. Furthermore, the high efficiency of mist injection enables the device to be driven at a low voltage, thereby achieving low power consumption. As a result, the heat generation of the piezoelectric members 30 and 31 can be suppressed to a low level, and the damage to the ink can be reduced by suppressing the cavitation as much as possible, whereby the composition separation of the ink and the adhesion of the ink components to the surface of the piezoelectric member can be prevented. Can be reduced. Therefore, the piezoelectric members 30, 31
It is possible to maintain the vibration and the mist formation of ink in a stable state. In addition, two piezoelectric members 3 that are oscillation sources
Since 0 and 31 are independently provided for each ink chamber 27, vibration does not affect adjacent ink chambers to cause crosstalk, and stable mist ejection can be performed for each ink chamber 27.

By the way, in the above embodiment, the pulse voltage shown in FIG. 8A was applied to the piezoelectric members 30 and 31, but the number, voltage value, frequency, etc. of the original pulses 52 constituting the pulse voltage are adjusted. By doing so, it is possible to change the generation amount and the particle size of the ink mist, which enables halftone reproduction. For example, when the pulse voltage shown in FIG. 8B is applied, the number of original pulses 52 included is large and the number of vibrations of the piezoelectric members 30 and 31 is increased as compared with the pulse voltage shown in FIG. 8A. The amount of ink mist increases, and the density of ink adhering to the recording paper increases. FIG.
According to the pulse voltage shown in (c), by lowering the voltage of the bottom line of the original pulse 54 in the middle, low voltage driving becomes possible, and the driver cost can be reduced. Further, as shown in FIG. 8D, according to the pulse voltage (the AC voltage is also acceptable) whose polarity alternates, the piezoelectric member 3
The amplitude width of 0 and 31 becomes large, and a larger vibration energy can be obtained.

As the shape of the original pulse forming each of the pulse voltages, other than the shape shown in FIG. 8 (e), FIG.
It is also possible to use a falling portion 55 shown in FIG. According to the original pulse of this shape, the piezoelectric members 30, 3
The restoring operation of No. 1 is slightly delayed, and there is an effect of preventing the ink meniscus surface 53 from being excessively drawn in the nozzle hole 26a and sucking bubbles into the ink chamber 27. Further, as shown in FIG. 8G, if the original pulse in which the voltage line in the off state is constantly raised is used, the driver cost can be reduced by the low voltage driving. 8 (e) and (f)
8 (h) and 8 (i) may be used for the original pulse shown in FIG. According to these original pulses, the piezoelectric members 30 and 31 are slipped and deformed in a direction in which their upper portions are separated from each other when the voltage is on, and vibrate by repeating the elastic restoring operation when the voltage is off. Here, the reason why the pulse-shaped falling portion 56 shown in FIG. 8 (i) is inclined is the same as in the case of FIG. 8 (f).

Next, FIG. 11 shows a modification of the above embodiment.
This will be described with reference to FIGS. In the above embodiment, the surface of the piezoelectric members 30 and 31 on which the electrodes are not formed is the substrate 2
1 was bonded and fixed to the piezoelectric member 3 as shown in FIG.
The surface on which the second electrodes 38 and 39 of 0 and 31 are formed is adhered and fixed to the substrate 21 through the conductive adhesive layer 57, and the adhesive layer 5 is formed.
Even if a pulse voltage is applied to 7, the piezoelectric members 30 and 31 can obtain the same vibration as in the above embodiment.

On the other hand, the modified example shown in FIG.
The directions of adhesion of 0 and 31 to the substrate 21 and the direction of electric field formation by voltage application are the same as those of the modification shown in FIG.
As shown by arrows in FIG. 12, the piezoelectric members 30 and 31 are polarized in the directions from the second electrodes 38 and 39 to the first electrodes 35 and 36, respectively. In this case, each of the piezoelectric members 30 and 31 is deformed based on a so-called thickness direction vibration mode, contracts and deforms in the width direction by applying a voltage, and expands and deforms in the thickness direction. Even when such deformation is repeated at high speed, high-frequency vibration energy is generated, and the ink can be misted and ejected.

In the above embodiment, one ink chamber 2 is used.
Although the two piezoelectric members 30 and 31 are arranged for each of the seven, the present invention is not limited to this, and as shown in FIG. 13 or 14, for example, three or four piezoelectric members 60 to 62, 63 per ink chamber 27 are provided. The elements 66 to 66 may be arranged on the substrate 21 so as to face each other, and the same effects as those of the above-described embodiment can be obtained. Also in this case, the nozzle hole 26a is formed corresponding to approximately the center of the triangular or rectangular area surrounded by the piezoelectric members.

[0027]

As is apparent from the above description, according to the ink jet recording apparatus of the present invention, two or more piezoelectric members, which are oscillation sources, are arranged on the substrate of the ink chamber so as to face each other, and respectively. By oscillating in a synchronized manner, high-frequency vibration energy is sandwiched between the piezoelectric members,
Alternatively, the ink can be concentrated in almost the center of the enclosed area, and the ink can be efficiently misted and ejected. In this case, if a nozzle is formed at a position on the nozzle plate corresponding to the central portion, it can be used for forming mist of ink without loss of concentrated high frequency vibration energy, and more efficient ink mist ejection is possible. become.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an inkjet recording apparatus.

FIG. 2 is a cross-sectional view of an inkjet head.

FIG. 3 is a partially enlarged view of a cross section of the inkjet head shown in FIG.

FIG. 4 is a diagram for explaining preferable dimensional conditions regarding a piezoelectric member.

FIG. 5 is a diagram for explaining preferable dimensional conditions regarding the piezoelectric member, similar to FIG.

6 is a cross-sectional view taken along the line IV-IV of the inkjet head shown in FIG.

FIG. 7 is a partial perspective view of an inkjet head fixed on a head base.

FIG. 8 is a diagram illustrating a pulse voltage applied to a piezoelectric member and a shape of an original pulse forming the pulse voltage.

FIG. 9 is a diagram for explaining a deformed state of the piezoelectric member due to voltage application.

FIG. 10 is a cross-sectional view of the inkjet head showing a state where ink mist is ejected from the nozzle holes.

FIG. 11 is a diagram showing a modified example of the bonding direction of the piezoelectric member to the substrate.

12 is a diagram showing another modification example in which the polarization direction of the piezoelectric member is different from the modification example of FIG.

FIG. 13 is a diagram showing a modified example in which three piezoelectric members are arranged for each ink chamber.

FIG. 14 is a diagram showing a modified example in which four piezoelectric members are arranged for each ink chamber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ink jet recording device, 6 ... Controller (voltage application means), 21 ... Substrate, 26 ... Nozzle plate, 26
a ... Nozzle hole (nozzle), 27 ... Ink chamber, 30, 31
... Piezoelectric member.

Claims (2)

[Claims] 1. An ink chamber formed between a substrate and a nozzle plate having nozzles, two or more piezoelectric members arranged on the substrate of the ink chamber so as to face each other, and each piezoelectric member. And voltage applying means for synchronously applying a high frequency pulse voltage having a frequency equal to or higher than the natural frequency of the piezoelectric member according to the image signal, and applying a voltage to the piezoelectric member by the voltage applying means to cause high frequency vibration. An ink jet recording apparatus in which the ink filled in the ink chamber is formed into a mist and ejected from a nozzle. 2. The ink jet recording apparatus according to claim 1, wherein the nozzle is sandwiched by the piezoelectric members or formed at a position of a nozzle plate corresponding to a substantially central portion of an enclosed area.