Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-05-15
2002-10-22
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06467886
ABSTRACT:
TECHNICAL FIELD
The present invention belongs to a technical field involving an ink jet head which utilizes piezoelectric actuators to discharge ink through its nozzles, a method for fabricating the ink jet head, and an ink jet recording device.
BACKGROUND ART
An ink jet head which utilizes piezoelectric actuators to discharge ink is a known art, and may comprise a head main body
101
including a plurality of hollows
102
as pressure rooms each having an inlet
102
a
for ink supply and an outlet
102
b
for ink discharge as shown in FIG.
9
. The hollows
102
are arranged at regular intervals in one direction (perpendicular to the paper) in the head main body
101
.
The head main body
101
is composed of a pressure room component
105
forming the side walls of the hollows
102
, an ink path component
106
which forms the bottom wall of the hollows
102
and is made by bonding a plurality of thin plates together, and a nozzle plate
113
. The ink path component
106
includes paths
107
for ink supply and paths
108
for ink discharge, which are connected with the inlets
102
a
and outlets
102
b,
respectively. The paths
107
for ink supply are connected to an ink supply room
110
extending in the direction in which the hollows
102
are arranged, and the ink supply room
110
is connected to an ink supply hole
111
, which is formed in the pressure room component
105
and ink path component
106
, and is connected with an ink tank outside the drawing. The nozzle plate
113
is provided with nozzles
114
connected with the paths
108
for ink discharge.
On the top surface of the pressure room component
105
of the head main body
101
, piezoelectric actuators.
121
are provided in such a manner as to block the hollows
102
of the head main body
101
, thereby making up pressure rooms
103
with the hollows
102
. The piezoelectric actuators
121
include piezoelectric elements
123
and top electrodes
124
provided on the surfaces of the piezoelectric elements
123
that are opposite to the pressure rooms
103
side. In addition, a bottom electrode
122
is provided on the surfaces of the piezoelectric elements
123
that are on the pressure rooms
103
side. The single bottom electrode
122
is shared by all the piezoelectric actuators
121
, and also functions as a so-called diaphragm.
Applying a pulse-like voltage between the bottom electrode
122
and the top electrodes
124
causes the piezoelectric elements
123
to contract in the direction perpendicular to the direction of their thickness due to electric fields developing inside the piezoelectric elements
123
. On the other hand, the bottom electrode
122
and top electrodes
124
do not contract, so that a so-called bimetal effect makes the portions of the piezoelectric actuators
121
that correspond to the pressure rooms
103
deform to bend toward the pressure rooms
3
side. This deformation generates pressure inside the pressure rooms
3
, and makes the pressure discharge the ink in the pressure rooms
3
outside through the nozzles
114
via the outlets
102
b
and paths
108
for ink discharge.
By the way, such ink jet heads that utilize piezoelectric actuators to discharge ink through the nozzles have been variously improved in recent years to meet the stringent demands for reduction in size, driving voltage, noise, cost, improvement in ink discharge control, and the like. In order to achieve further downsizing and higher performance, it is possible to form the piezoelectric elements and electrodes into thin films, which can be micromachined easily. The easiest and most reliable method for forming these thin films is first to form the top electrodes, piezoelectric elements, and bottom electrode in this order on a substrate by spattering or deposition, then to fix the bottom electrode thus formed to the head main body, and later to eliminate the substrate by etching or another process.
However, the spattering or deposition undesirably develops foreign particles during the film formation, which cause minute defective portions in indefinite regions in the piezoelectric elements in such a manner as to be isolated by cracks from the other parts. Above all, in the case of spattering, unevenness in discharge or potential in the initial stages of the spattering can trigger to cause more such defective portions. The defective portions gradually grow as the film formation proceeds, making the cracks be extended and tapered down in the thickness direction of the piezoelectric elements. These cracks usually have approximately circular openings on both surfaces of the piezoelectric elements in their thickness direction (penetrating the piezoelectric elements in their thickness direction). Moreover, forming the bottom electrode onto the piezoelectric elements by spattering or deposition makes the bottom electrode have defective portions, which are caused by and contiguous with the defective portions in the piezoelectric elements. As a result, the bottom electrode has cracks contiguous with the cracks in the piezoelectric elements. The bottom electrode further has similar defective portions, which are caused in regions not contiguous with the defective portions of the piezoelectric elements. When the bottom electrode is made from chrome preferably used for its excellent ink discharge performance and other characteristics in order to function the electrode as a diaphragm, defective portions occur much more easily. Although the occurrence of these defective portions can be restricted to some extent, it is difficult to eliminate them completely.
The presence of the defective portions (cracks) in the piezoelectric elements decreases their mechanical strength, and increases the intensity of the electric fields in the cracks, thereby promoting leaks. The presence of cracks in the bottom electrode decreases its mechanical strength, and makes it impossible to uniformly apply a voltage on the entire piezoelectric elements. Moreover, if the ink in the pressure rooms happens to be in contact with the piezoelectric elements via the cracks in the bottom electrode, the piezoelectric elements may be melted or damaged in other ways, depending on the material of the ink. If cracks are formed contiguously across the piezoelectric elements and bottom electrode, intrusion by ink having less electric insulation than the piezoelectric elements may cause a short between the bottom and top electrodes, so as to produce a dielectric breakdown.
The present invention has been contrived in view of these aspects, and its object is that when an ink jet head is downsized by forming the piezoelectric elements and electrodes of the piezoelectric actuators into thin films, the piezoelectric actuators are prevented from malfunctioning due to the cracks developing in the piezoelectric elements or electrodes during the film formation, so as to increase their durability.
DISCLOSURE OF THE INVENTION
In order to achieve the above-mentioned object, according to the present invention, the piezoelectric actuators, which include piezoelectric elements, first electrodes provided on the surfaces of the piezoelectric elements that are opposite to the pressure rooms side, and a second electrode provided on the other surfaces of the piezoelectric elements that are on the pressure rooms side, further comprise either a crack covering member or an ink contact prevention member either on the surface of the second electrode that is on the pressure rooms side or on the surfaces of the piezoelectric elements that are on the second electrode side. The crack covering member is made from an electric insulating material, which is used to fill a crack, whereas the ink contact prevention member prevents the ink in the pressure rooms from being in contact with the piezoelectric elements via the crack in the second electrode.
To be more specific, the first invention relates to an ink jet head comprising: a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet; and a piezoel
Matsuo Hiroyuki
Takao Shigeyuki
Tomita Kenji
Watanabe Osamu
Harness & Dickey & Pierce P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Vo Anh T. N.
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