JP2979665B2 - Inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer for selectively depositing ink droplets on an image recording medium.

[0002]

2. Description of the Related Art The structure of a conventional inkjet head is as follows.
JP-A-63-252750 or JP-A-63-252750
No. 2,470,51.

These are composed of a number of parallel flow paths which are spaced from each other in the direction in which the ink discharge nozzles are arranged. The flow paths are located on the top, the bottom, in the longitudinal direction of the flow path and in both the longitudinal direction and the nozzle arrangement direction. It is delimited by vertically extending side walls. One end of the flow path is connected to a nozzle plate having a plurality of nozzles, and the other end has an ink supply port connected to ink supply means for replenishing each channel with ink.
The side wall is partially or entirely made of a piezoelectric material,
The electric actuating means causes a deformation in a shear mode or the like parallel to the array direction, changes the pressure of ink using the flow path as a pressure generating chamber, and ejects ink droplets from nozzles.

[0004]

However, when the flow paths are integrated at a high density, the width and the cross-sectional area of the flow path become smaller, and the flow path resistance increases. Further, since the amount of deformation of the side wall is small, it is necessary to increase the length of the flow path in order to secure a required amount of ink ejection. Therefore, in the related art in which the nozzle is formed at one end of the flow path and the ink supply port is formed at the other end,
Since the flow path resistance across the entire flow path contributes to supply the reduced amount of ink from the ink storage tank by the ink discharge, the ink supply speed is low, and the repetition frequency of ink ejection cannot be increased. Has problems. Also, the ratio of the long side to the short side of the cross section of the flow path is large,
Since the flow path is long, there is a problem that air bubbles easily stay in the flow path and ink is not easily discharged due to pressure absorption by the air bubbles.

An object of the present invention is to solve these problems, and an object of the present invention is to provide an ink jet head having high density, a high number of nozzles, and high reliability and stability. .

[0006]

The ink jet head of the present invention has a number of parallel flow paths spaced from each other in the direction in which the ink discharge nozzles are arranged, and the top, bottom, and part of the side walls of the flow paths. Alternatively, an electrode is formed on the entire surface, and the side wall is partially or entirely made of a piezoelectric material, and the pressure in the flow path is changed by deformation of the side wall by an electric actuating means, thereby forming the side wall of the flow path. In an ink jet head for ejecting ink droplets from a nozzle formed near one end, an ink discharge port is formed near another end where the nozzle of the flow path is not formed, and an ink supply port is formed in the middle of the flow path. The ink discharge port is connected to ink suction means, and the ink supply port is connected to an ink storage tank.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below.

FIG. 1 is a perspective view of one embodiment of the present invention, showing the internal structure by a partial cross section. In FIG. 1, 1
Is a piezoelectric substrate, 2 is a nozzle forming member, 3 is a nozzle, 4 is a flow path, 5 is a side wall, 6 is an upper substrate, 7 is an ink supply port, 8 is a slit substrate, and 9 is an ink discharge port.

The piezoelectric substrates 1a and 1b polarized in the thickness direction
Are joined so that the polarization directions are opposite to each other,
800μ depth using diamond cutting disk
A large number of mutually parallel flow paths 4 having a width m of 100 μm and a pitch of 169 μm are formed. By setting the thickness of the substrate 1b to 400 μm, the side walls 5 defining the adjacent flow paths 4 are symmetric with respect to the bonding surface. One end of the flow path 4 is connected to the nozzle 3 formed on the nozzle forming substrate 2, and the other end of the flow path 4 is passed through a slit-shaped ink discharge port 9 formed by a slit substrate 8 and is supplied with ink suction means. Connect to a rotary pump (not shown). The flow path 4 is covered with an upper substrate 6 having an ink supply port 7 corresponding to the flow path pitch, and is passed through an ink supply port 7 corresponding to each flow path 4 to an ink storage tank (not shown). Connected.

When a voltage pulse is applied from an electric actuating means (not shown) between electrodes (not shown) formed on both sides of a side wall 5 defining each flow path 4, the side wall 5 is deformed and generated. Due to the applied pressure, a part of the ink filling the flow path 4 is ejected from the nozzle 3 as ink droplets, and the other part is discharged to the ink storage tank side via the ink supply port 7. At this time, since the flow path resistance of the ink discharge port 9 is sufficiently larger than the nozzle 3 and the ink supply port 7, the outflow of ink to the ink discharge port 9 is small. As a means for sufficiently increasing the flow path resistance of the ink discharge port 9 at the time of ink droplet discharge, a method of forming the slit-shaped ink discharge port 9 having a high flow path resistance as in this embodiment, or a method of discharging the ink at the time of ink drop discharge. A method in which the outlet is closed by actuating means is also applicable. After the ink droplets are ejected, the ink is supplied to the nozzle portion from the ink storage tank through the ink supply port 7 and the flow path 4 by the capillary force of the nozzle 3. At this time, the ink supply path does not pass through the flow path 4 from end to end, but extends from the middle of the flow path 4 to one end connected to the nozzle 3, so that the ink supply path is short and the flow path resistance is low. Therefore, the time required for supplying the ink to the nozzle 3 is reduced, and the repetition frequency of the ink droplet ejection is about 10 k.
Hz.

In the ink jet head according to the present embodiment in which the ink is ejected by the generation of pressure due to the deformation of the flow path, the ink must completely fill the inside of the flow path 4, and bubbles will be generated inside the flow path 4. If it is present, the generated pressure is absorbed by the bubbles, and ink cannot be ejected.

In this embodiment, when ink is initially filled in the flow path 4, a rotary pump (not shown) serving as an ink suction means is used to supply ink from the ink discharge port 9 to the inside of the flow path 4. No air bubbles remain because the air is sucked. Since air bubbles entering when replacing the ink storage tank can be removed, a highly reliable ink jet head can be constructed. Also,
The ink that fills the flow path 4 between the ink supply port 7 and the ink discharge port 9 moves little during normal ink discharge, and the ink deteriorates over a long period of time. Ink supply port 7 using
By discharging the ink filling the flow path 4 between the ink and the ink discharge port 9, stable ink characteristics could be secured.

Next, the operation principle of the ink jet head of this embodiment will be outlined with reference to FIG. In FIG. 2A, electrodes 40a and 40b formed in the same flow path 4
Are electrically connected to each other and are connected to a driving driver element 70 which is an electric actuating means for each channel. The driver element 70 is provided with a control signal 72 from the control unit 71.
, A high voltage output or a low voltage output from the DC power supply 73 is selectively supplied to the electrodes 40 in each flow path 4. Each flow path 4 is grouped into two, one skipped (even number and odd number), and each group is partitioned by time and driven alternately. As shown in FIG. 2B, the deformed portion 36, which is a side wall that divides the selected flow path 4a and its adjacent flow path 4b, is selected so as to be orthogonal to the polarization directions 50 and 51 of the piezoelectric substance. When the driver element connected to the selected flow path 4a and the adjacent flow path 4b is controlled, the deforming portion 36 made of the piezoelectric material is deformed in the shear mode, and the volume of the selected flow path 4a is reduced and the flow path 4a is reduced. A pressure is generated in the ink 61 to be filled. The generated pressure propagates in the flow path 4a and causes ink droplets to be ejected from a nozzle (not shown).

In the embodiments described below, the basic operation principle is the same as that of FIG.

FIG. 3 is a longitudinal sectional view of a flow channel showing another embodiment of the present invention. In FIG. 3, 12 is a nozzle forming member, 13 is a nozzle, 14 is a flow path, 17 is an ink supply port, 19 is an ink discharge port, and 24 is a pressure absorbing chamber.

In this embodiment, the nozzle 13 and the ink discharge port 19 are formed near both ends of the flow path 14 in a direction perpendicular to the longitudinal direction of the flow path 14. In the present invention, since the flow path resistance between the nozzle 3 and the ink supply port 17 is low, the ink supply speed is high, but on the other hand, the pressure generated in the flow path 14 propagates to the adjacent flow path, and the pressure between the adjacent elements increases. Crosstalk is likely to occur.
In this embodiment, before each ink supply port 17 is connected to an ink supply unit (not shown) common to each flow path,
Providing the pressure absorption chamber 24 for the pressure suppressor 4 suppresses the pressure propagation to the adjacent flow passage, and enables high integration of the flow passage.

[0017]

As described above, according to the present invention, an ink discharge port is formed near the other end of the flow path where the nozzle is not formed, so that the ink can be initially filled into the flow path and the ink can be discharged. This has the effect that it is easy to remove bubbles in the flow path when replacing the storage tank. Further, the ink staying in the flow path for a long time can be periodically removed, and the ink characteristics can be kept constant. Further, by forming the ink supply port in the middle of the flow path, the flow path resistance from the ink supply port to the nozzle is reduced, the ink supply speed to the nozzle portion is increased, and the repetition frequency of ink discharge can be increased. Has an effect.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one structure of an embodiment of the present invention by a partial cross section.

FIG. 2 is an explanatory diagram showing the operation principle of the ink jet head of the present invention.

FIG. 3 is an explanatory diagram showing a cross section of one structure of the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2, 12 Nozzle formation substrate 3, 13 Nozzle 4, 14 Flow path 5 Side wall 7, 17 Ink supply port 9, 19 Ink discharge port 24 Pressure absorption chamber

Claims (1)

(57) [Claims] A plurality of parallel flow paths spaced from each other in a direction in which the ink discharge nozzles are arranged; electrodes are formed on part or all of the top, bottom and side walls of the flow paths; Is partially or entirely made of a piezoelectric material, and changes the pressure in the flow path by deformation of the side wall by the electric actuating means, so that an ink droplet is formed from a nozzle formed near one end of the flow path. In the ink jet head to be ejected, an ink outlet is formed near the other end of the flow path where the nozzle is not formed, an ink supply port is formed in the middle of the flow path, and the ink discharge port is connected to ink suction means. And an ink supply port connected to an ink storage tank.