Ink jet print head having homogeneous base plate and a method of manufacture

An ink jet print head 10 of the invention comprises a base plate 12 which includes a nozzle hole 14 and an ink supply channel 20 in one surface thereof and an actuator 30 which is bonded on the one surface of the base plate 12 to cover the nozzle hole and ink supply channel. The actuator 30 is formed in one surface adjacent to the base plate with an ink chamber 32 which connects the ink supply channel 20 and the nozzle hole 14. The ink chamber 32 and nozzle hole 14 are filled with an ink material, and the ink material is ejected through the nozzle hole 14 when it is pressurized by the actuator 30. According to the ink jet print head 10 of the invention, the number of parts constituting the head can be reduced, and a shorter production process and a lower production cost can be achieved.

FIELD OF THE INVENTION 
The present invention relates to an ink jet print head for recording an 
image by ejecting ink droplets from nozzles in response to image 
information, and allowing the ink droplets to be deposited to such 
recording medium as plain paper. 
BACKGROUND OF THE INVENTION 
Conventionally, there has been known an ink jet print head which includes 
piezoelectric actuators or members and a housing corresponding to the 
piezoelectric actuator. The housing has a chamber for containing an ink 
material and a nozzle for ejecting ink droplets of the ink material. In 
operation, a voltage or pulse is applied to the piezoelectric member in 
response to information corresponding to an image to be reproduced. This 
provides the piezoelectric member with a deformation, which pressurizes 
the ink material in the ink chamber and thereby eject the ink droplet 
through the nozzle. 
Another ink jet print head has been proposed in which a diaphragm made from 
film is disposed between the piezoelectric member and the ink chamber so 
that the piezoelectric member is kept away from the ink material. 
In these ink jet print heads, the ink chambers are formed in a uniform 
array at a regular interval. This requires that the piezoelectric members 
be arranged so that each piezoelectric member confront to the 
corresponding ink chamber. For this purpose, typically, the piezoelectric 
members are formed by firstly bonding a sintered piezoelectric plate onto 
a base plate and secondly cutting the piezoelectric plate into parallel 
pieces by the use of a suitable cutter or saw. 
This piezoelectric member, as it is made of two components and further the 
components are bonded with adhesive, renders the manufacturing process 
thereof more complicated and requires more time for producing the same and 
decreases a yield rate of the piezoelectric member, which results in the 
print head being more expensive. Also, cutting the sintered piezoelectric 
plate requires an extended time and tends to reduce the productivity of 
the piezoelectric member, which further increases the production cost of 
the same. 
SUMMARY OF THE INVENTION 
Among the several objects and features of the invention may be noted the 
provision of an improved ink jet print head. 
An ink jet print head 10 of the invention comprises a base plate 12 which 
includes a nozzle hole 14 and an ink supply channel 20 in one surface 
thereof and an actuator 30 which is bonded on the one surface of the base 
plate 12 to cover the nozzle hole 14 and ink supply channel 20. The 
actuator 30 is formed in one surface adjacent to the base plate 12 with an 
ink chamber 32 which connects the nozzle hole 14 and the ink supply 
channel 20. The ink chamber 32 and nozzle hole 14 are filled with an ink 
material, and the ink material is ejected through the nozzle hole 14 when 
it is pressurized by the actuator 30. 
According to an ink jet print head 10 of the invention, the ink chamber 32 
is formed in one surface of the actuator 30, and the nozzle hole 14 for 
ejecting the ink material and the ink supply channel 20 for supplying the 
ink material to the ink chamber 32 are formed in a base plate 12. In such 
manner, a main part of the ink jet print head is constituted simply by the 
base plate 12 and the actuator 30, and the number of parts of the head can 
be reduced. As a result, assembly of the head is completed in fewer steps, 
and a lower production cost and a higher yield rate can be achieved. 
In another ink jet print head 50 of the invention, the base plate 12 is 
further provided with a groove 52 which defines an ink supply chamber 42 
connected with the ink supply channel 20. 
According to the ink jet print head 50 of the invention, in addition to an 
effect similar to that obtained by the ink jet print head 10, because a 
groove 52 in communication with ink supply channel 20 is formed in a base 
plate 12, and the groove 52 is used as the ink supply chamber 42 for 
supplying the ink material to the ink chamber 32 in actuator 30 through 
the ink supply channel 20, it is not required to use a component 
configured specifically for forming the ink supply chamber 42, as a 
result, further reduction of cost can be achieved. 
Still another embodiment of the present invention is ink jet print head 110 
comprising a member 112 which includes a nozzle hole 124 for ejecting an 
ink material, an ink chamber 130 in fluid communication with the nozzle 
hole 124 for supplying the ink material to the nozzle hole 124, and an ink 
supply channel 128 for supplying the ink material to the ink chamber 130. 
The nozzle hole 124, ink chamber 130 and ink supply channel 128 form an 
ink passage 133. The ink jet print head 110 further comprises an actuator 
114 which is activated to pressurize the ink material in the ink chamber 
130 and eject the ink material from the nozzle hole 124. The member 112 is 
made of a plurality of layers which are integrated by heating, and each of 
the layers defines at least one portion of the ink passage 133. 
In the ink jet print head 110 according to the invention, the layers which 
define portions of the ink passage 133 are integrated upon burning of the 
actuator 114. The actuator 114 is also bonded integrally to the member 112 
when the actuator 114 and the member 112 are burned. Accordingly, since no 
application of an adhesive is required in any step during assembly of the 
head, and the layers and the actuator 114 can be bonded integrally to each 
other in a single heating operation, a process of assembly can be 
simplified. As a result, an efficiency of producing a head is increased, 
and a lower production cost can be achieved.

PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to the drawings, embodiments of the invention will be described 
below. An ink jet print head 10 of a first embodiment is shown in FIGS. 1 
and 2. The head 10 comprises a base plate 12 in the form of plate made of 
a ceramic, metal, glass, synthetic resin or the like. The base plate 12 is 
formed with a plurality of nozzle holes 14 at certain intervals, extending 
in the direction of thickness thereof. Each nozzle hole 14 is formed 
through two steps, as described later, and comprises a first portion 16 
and a second portion 18, the second portion 18 being smaller in diameter 
than the first portion 16. In an upper surface of the base plate 12, a 
plurality of ink supply grooves or channels 20 are formed in 
correspondence with the nozzle holes 14. The ink supply channel 20 is 
spaced away from the nozzle hole 14 and is extended toward the nozzle hole 
14, as illustrated in FIG. 3 which is a partial top plan view of the base 
plate 12 before it is assembled in the head 10. 
On a lower surface of the base plate 12, an eutectoid plating 22 containing 
fluorine is deposited. Due to this, an ink repellent property is 
increased, which results in that an ink meniscus to be formed in the 
second portion 18 of nozzle hole 14 will be stabilized and thereby ink 
droplets having a required size can be ejected. An improved adhesion can 
be provided to the base plate 12 made of a ceramic or metal against the 
eutectoid plating 22. 
To the upper surface of the base plate 12, a plurality of piezoelectric 
actuators 30 made from any known piezoelectric material is fixedly bonded. 
The piezoelectric actuator 30 is formed in a portion thereof facing the 
base plate 12 with an ink chamber 32 which is an elongated groove that is 
closed at both longitudinal ends thereof. The ink chamber 32 is in 
communication with a corresponding one of the nozzle holes 14 and an end 
of the ink supply channel 20 adjacent to the nozzle hole 14, respectively. 
An inner wall of the ink chamber 32 is lined with a common electrode 34 
made of a conductive metal layer. As shown in FIG. 2, the common electrode 
34 is extended to respective upper surface portions of longitudinal 
opposite ends of the piezoelectric actuator 30. One extended portion 36 of 
the common electrode 34 located adjacent to the nozzle hole 14 is 
connected with a negative terminal (for example, a ground terminal) of a 
drive circuit through a flexible wiring (not shown). Also, the 
piezoelectric actuator 30 is provided on a central portion of the other 
surface or upper and side surfaces away from the ink chamber 32 with an 
individual electrode 38. The individual electrode 38 is extended 
longitudinally and connected with a positive terminal of the drive circuit 
through a flexible wiring (not shown). 
An ink supply member 40, which is fluidly connected with an ink tank (not 
shown), is fixed on the base plate 12 in contact with longitudinal end 
surfaces of the piezoelectric actuators 30. The ink supply member 40 has 
herein an ink supply chamber 42. The ink supply chamber 42 is fluidly 
communicated with each ink chamber 32 of the piezoelectric actuator 30 
through the ink supply channels 20. 
The ink jet print head 10 so constructed will be produced as described 
below. First, the nozzle holes 14 and ink supply channels 20 are formed in 
the base plate 12 which is already provided at a lower surface thereof 
with the eutectoid plating 22. In this forming process, a conventional 
excimer laser beam machining is preferably available if the base plate 12 
is made of a ceramic. The nozzle hole 14 is formed in two steps, a first 
step in which a first laser beam is illuminated to form a first portion 16 
having a diameter approximately equal to that of the laser beam and a 
second step in which another laser beam having a diameter smaller than 
that of the first laser beam is illuminated to form the second portion 18 
having a diameter approximately equal to that of the second laser beam. 
Instead of the laser beam machining, another technique may be employed for 
forming the first portion 16 of the nozzle hole 14 such as etching, 
cutting by abrasive grains using ultrasonic vibration of a cemented 
carbide mold and punching to a green sheet before sintering thereof. 
Next, a piezoelectric plate is formed with a plurality of grooves for 
providing the ink chambers 32 in correspondence with the nozzles 14 and 
ink supply channels 20 by the excimer laser beam machining, then 
metal-plated to provide the common electrode 34 on an inner surface of 
each groove, and finally bonded to an upper surface of the base plate 12. 
After the bonded piezoelectric plate is divided into a plurality of 
piezoelectric actuators 30 in such manner that a plurality of separated 
grooves 44 are formed in the piezoelectric plate by the laser machining or 
dicing, a conductive metal layer to be used for the individual electrode 
38 is formed on an outer circumference thereof by plating or sputtering. 
Production and assembly of a main part of the ink jet print head 10 is now 
completed, and the ink supply member 40 is finally fixed to the base plate 
12. 
In the ink jet print head 10 so constructed, an ink material supplied from 
the ink tank to the ink supply chamber 42 is fed to the ink chambers 32 in 
the piezoelectric actuators 30 and the nozzle holes 14 through the ink 
supply channels 20. Then, when a voltage or pulse is applied between the 
individual electrode 38 and common electrode 34 by the drive circuit, a 
portion of the piezoelectric actuator 30 that is located in correspondence 
with the individual electrode 38 and forms three walls defining a portion 
of the ink chamber 32 is instantaneously deformed inwardly as shown by a 
dotted line 48 in FIG. 1. This pressurizes the ink material in the ink 
chamber 32, and thereby an ink droplet is ejected through a nozzle opening 
15 in the base plate 12. The ink droplet is then deposited onto a 
recording medium, such as plain paper (not shown), and thereby an image is 
recorded on the recording medium. 
As described above, according to the ink jet print head 10 of this 
embodiment, the main portion of the head is constituted simply by the base 
plate 12 and piezoelectric actuators 30. Therefore, the number of parts 
can be significantly reduced in comparison with the conventional head, and 
a cost for the parts can be reduced. Further, since assembly can be 
completed in fewer steps and the number of possible defects at assembling 
will be reduced, a higher yield rate can be achieved, and time required 
for assembling will be reduced, resulting in a lower production cost. 
In the mean time, the piezoelectric plate may be used without being cut 
into a plurality of piezoelectric actuators. In such case, individual 
electrodes are provided on portions of an upper surface of the 
piezoelectric plate corresponding to the ink chambers and only these 
portions will be driven. 
With reference to FIGS. 4 and 5, another ink jet print head 50 of the 
second embodiment will be described. The ink jet print head 50 is similar 
in construction to that of the first embodiment with respect to the base 
plate 12 and piezoelectric actuators 30, and therefore only distinctive 
characteristics are described. 
In a base plate 12 of the ink jet print head 50, a groove 52 is formed in 
communication with ends of the ink supply channels 20 which ends are 
remote from nozzle holes 14, as illustrated in FIG. 6 which is a partial 
top plan view of the base plate 12 before it is assembled in the head 50. 
The groove 52 is covered by a cover plate 54 to define an ink supply 
chamber 42 surrounded thereby. The ink material is supplied from the ink 
supply chamber 42 to the ink chambers 32 through the ink supply channels 
20. 
Thus, with the ink jet print head 50, since the ink supply chamber 42 is 
also provided in the base plate 12, it is not required to use such 
component of a specific shape as the ink supply member 40 in the first 
embodiment that is provided therein with a hollow area, and a cost for 
parts can be further reduced. 
Although the nozzle holes 14 are formed to be reduced in size between the 
first portion 16 and the second portion 18 in the first and second 
embodiments, they are not limited to such shape, and may be formed, for 
example, in such manner that the inner diameter is progressively reduced 
from the ink chambers 32 to the nozzle openings 15 in the lower surface of 
the base plate 12. The ink supply channels 20 may be also formed, for 
example, in such manner that they are reduced in width toward the ink 
supply chamber 42 instead of having a constant width. In this case, a back 
pressure caused toward the ink supply chamber 42 upon driving of the 
actuator can be reduced, and a driving force of the actuator can be more 
efficiently utilized. 
Next, an ink jet print head 110 according to a third embodiment will be 
described by referring to FIGS. 7 to 9. The head 110 comprises a channel 
unit 112 and piezoelectric actuators 114. The channel unit 112 is formed 
by laminating four ceramic layers 116, 118, 120 and 122 that are delimited 
by dotted lines in sectional views shown in FIGS. 8 and 9, and the layers 
are bonded integrally to each other by sintering. The channel unit 112 is 
further provided with ink channels 133 comprising nozzles 124, 
communicating holes 126, ink supply channels 128, ink chambers 130 and an 
ink supply chamber 132. 
The ceramic layers 116, 118, 120 and 122 include portions that partly form 
the ink channels 133, respectively. In other words, in the first ceramic 
layer 116, a plurality of the nozzles 124 each in the form of a funnel are 
formed, and positioned in a staggered arrangement at regular intervals in 
both sides with respect to the ink supply chamber 132, as shown in FIG. 7. 
A water repellent finish is preferably applied to a lower surface of the 
first ceramic layer 116 for stabilization of an ink meniscus in the nozzle 
124. 
In the second ceramic layer 118, the communicating holes 126 are formed 
concentrically in such manner that they are in communication with the 
nozzles 124, respectively. Further in the second ceramic layer 118, the 
ink supply chamber 132, extending in a longitudinal direction in a central 
part of the head 110, and the ink supply channels 128, connecting the ink 
supply chamber 132 and the communicating holes 126, respectively, are 
formed. 
The ink supply chamber 132 is closed at an end (not shown), and connected 
with an ink tank (not shown) at an open end in the other side. 
In the third ceramic layer 120, the ink chambers 130 are formed, and 
connected with the communicating holes 126 and ink supply channels 128, 
respectively. The fourth ceramic layer 122 covers the ink chambers 130 so 
that it provides a wall thereof, and serves as a diaphragm. Additionally, 
a common electrode 134 made of a conductive metal layer is formed on an 
upper surface of the fourth ceramic layer 122. 
The piezoelectric actuators 114 each formed generally in the form of a disk 
are provided in correspondence with the ink chambers 130, respectively, on 
the common electrode 134 on a surface of the channel unit 112. Individual 
electrodes 136 made of a conductive metal layer are provided on the top of 
the piezoelectric actuators 114, respectively. 
Now, a process of producing the ink jet print head 110 so constructed will 
be described. The ceramic layers 116, 118, 120 and 122 are made of any 
known ceramic materials (for example, zirconium oxide, aluminum oxide), 
and individually processed when they are still green sheets before 
sintering. 
As shown in FIG. 10, an excimer laser beam illuminates a green sheet 140 to 
be the first ceramic layer 116 through a mask 144 with a plurality of 
openings 142 formed therein, and the nozzles 124 are formed by abrasion. 
As shown in FIGS. 11 and 12, a green sheet 146, to be the second ceramic 
layer 118, is punched by using a cemented carbide mold 148 to produce 
through-holes and grooves that are to be the communicating holes 126, ink 
supply channels 128 and ink supply chamber 132, respectively. The 
communicating holes 126 and ink supply channels 128 may be formed in both 
sides with respect to the ink supply chamber 132 by rotating the cemented 
carbide mold 148 or green sheet 146 for two steps of punching operation, 
or the cemented carbide mold 148 may be formed in such shape that the 
communicating holes 126 and ink supply channels 128 can be formed in both 
sides with respect to the ink supply chamber 132 by one step of punching 
operation. 
As shown in FIG. 13, similarly in a green sheet 150 that comes to be the 
third ceramic layer 120, rectangular through-holes are formed to provide 
the ink chambers 130 by punching. 
As shown in FIG. 14, to an upper surface of a green sheet 154 that comes to 
be the fourth ceramic layer 122, an electrode material, for example, an 
Ag-Pd paste is applied in a uniform thickness by screen printing or the 
like for providing the common electrode 134, and then a paste of any known 
piezoelectric material (for example, PZT) is applied on the electrode 
material by screen printing or the like to form the piezoelectric 
actuators 114. 
The green sheets 140, 146, 150 and 154 formed as described above are 
accurately aligned with each other by using a jig, respectively, as they 
are laminated in that order, and brought into close contact with each 
other by application of a pressure after they are laminated. Then, the 
laminated sheets are sintered in a heating furnace. The sintering 
operation is conducted in such conditions that the laminated sheets are 
heated to about 1200.degree. C. in 2 hours, for example, maintained at 
that temperature for 1.5 hours, and cooled spontaneously in the furnace. 
In such manner, the ceramic layers 116, 118, 120 and 122 and piezoelectric 
actuators 114 are sintered, and bonded integrally to each other. 
After the sintered product is removed from the heating furnace, the 
individual electrodes 136 are formed on top of the piezoelectric actuators 
114 by screen printing of an Ag-Pd paste, Au-sputtering or the like. Then, 
a high voltage is applied between the common electrode 134 and individual 
electrodes 136 under a high temperature for polarization of the 
piezoelectric actuators 114. 
Thus, according to the ink jet print head 110 of this embodiment, a 
plurality of ceramic layers 116, 118, 120 and 122 constituting the channel 
unit 112 and the piezoelectric actuators 114 are integrally bonded to each 
other upon sintering without using any adhesive. As a result, since 
application of adhesive is not required in any step during assembly of the 
ink jet print head 110, and the members can be simultaneously sintered and 
thereby bonded in single heating operation, a process of assembly and 
production of the head can be simplified, and a higher productivity and a 
lower production cost can be achieved. 
In the ink jet print head 110, an ink material supplied from an ink tank 
(not shown) to the ink supply chamber 132 is fed through the ink supply 
channel 128, and contained in the ink chamber 130, communicating hole 126 
and nozzle 124. In such state, when a voltage or pulse is applied between 
the individual electrode 136 and common electrode 134 by a driving circuit 
in response to an image signal, the piezoelectric actuator 114 is 
instantaneously deformed such that it is contracted in the radial 
direction. As a result of the deformation, as shown by a dotted line 158 
in FIG. 8, the fourth ceramic layer 122 is displaced arcuately, projecting 
in a convex manner toward the ink chamber 130. The ink material 
pressurized by the displacement is ejected as an ink droplet through the 
nozzle 124, and deposited to a recording medium (not shown), thus an image 
is recorded. As soon as application of the voltage is turned off, the 
piezoelectric actuator 114 and the wall of the ink chamber 130 return to 
their original state or undeformed state, and the ink material is supplied 
from the ink supply chamber 132 to the ink chamber 130. 
The lamination of ceramic layers in the channel unit 112 of the ink jet 
print head 110 described above is not limited to a of four layer 
configuration, and can be modified in various manners. 
Although the piezoelectric actuators are subjected to polarization using 
the individual electrodes provided after sintering in the third 
embodiment, if an electrode material for the individual electrodes is 
applied to the piezoelectric actuators by screen printing or the like 
before sintering, the individual electrodes can also be bonded at the same 
time, and a production process of the head can be further simplified. In 
such case, polarization of the piezoelectric actuators can be performed by 
applying a high voltage between the common electrode 134 and individual 
electrodes 136 after a predetermined time elapses and the piezoelectric 
material is crystallized. In such manner, processes including polarization 
of piezoelectric actuators can be completed in a single process, and a 
production process of the head can be further simplified. 
By referring to FIG. 15, an ink jet print head 160 according to a fourth 
embodiment will be described. FIG. 15 is an enlarged partial sectional 
view of the head 160 taken in the same direction as that of the ink jet 
print head 110 in FIG. 8, and a top plan view of the head 160 is generally 
similar to that of FIG. 7. 
As shown in FIG. 15, a channel unit 112 of the ink jet print head 160 
consists of a base plate 162 and an ink-chamber-forming member 164 layered 
on an upper part of the base plate 162, which are made of metallic 
materials, respectively. The base plate 162 is formed, for example, by 
Ni-electroforming, and provided with nozzles 124, communicating holes 126, 
an ink supply chamber 132 and ink supply channels 128 connecting the 
communicating holes 126 with the ink supply chamber 132. In the 
ink-chamber-forming member 164, hemispherical ink chambers 130 are formed 
in communication with the communicating holes 126 and ink supply channels 
128 by embossing, for example, a nickel sheet. Above the ink chamber 130, 
a piezoelectric actuator 114 having an individual electrode 136 thereon is 
provided. In the embodiment, the ink-chamber-forming member 164 can be 
used as a common electrode because of its conductivity. 
The base plate 162 and the ink-chamber-forming member 164 are integrally 
bonded to each other by diffusion bonding in respective contact surfaces 
as they are heated during sintering of the piezoelectric actuators 114. 
Accordingly, in this embodiment as well, similarly to the case of the ink 
jet print head 110, since the base plate 162, ink-chamber-forming member 
164 and piezoelectric actuators 114 can be bonded in a single heating 
operation without using any adhesive, a process of assembly of the head 
can be simplified, and a higher productivity and a lower production cost 
can be achieved. 
In the ink jet print head 160, when a voltage is applied between the 
individual electrode 136 and ink-chamber-forming member 164 by a drive 
circuit, the piezoelectric actuator 114 is deformed such that it is 
contracted in the direction of arrows 166. As a result of the deformation, 
an inner surface of the ink chamber 130 is displaced to a position shown 
by a dotted line 168, and thereby the ink material in the ink chamber 130 
is pressurized so that an ink droplet is ejected out of the nozzle 124. 
The ink-chamber-forming member 164 is not limited to the shape shown in 
FIG. 15, and can be modified in various manners. For example, the 
ink-chamber-forming member 164 may be shaped as if the third and fourth 
ceramic layers 120 and 122 in the ink jet print head 110 are integrally 
formed into ink-chamber-forming member 164. 
Although the present invention has been fully described by way of examples 
with reference to the accompany drawings, it is to be noted that various 
changes and modifications will be apparent to those skill in the art. 
Therefore, unless otherwise such changes and modifications depart from the 
scope of the present invention, they should be construed as being included 
thereto.