Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-24
2001-07-03
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S063000
Reexamination Certificate
active
06254215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing head adapted for use in an ink jet printer and a method for producing the same, and more particularly to an ink jet printing head in which, in forming nozzles and liquid chamber, the frame of the liquid chamber is constituted by the combination of walls having a width substantially equal to that of the nozzle wall, thereby improving adhesion of a heater board and a top plate and also improving the stability of manufacture, and a method for producing such ink jet printing head.
2. Related Background Art
For use in the ink jet printing head there have been proposed nozzles of various shapes, one of which will be explained with reference to FIG.
6
.
Referring to
FIG. 6
, a top plate
101
is formed from a silicon wafer which is cut and polished in such a manner that the upper face is constituted by the (
110
) crystalline plane. There are also shown a penetrating hole
102
constituting a liquid chamber or an ink reservoir, and a groove
103
for an ink discharging nozzle.
A silicon chip
108
is provided with a plurality of heat generating members (heaters)
109
and will be hereinafter called a heater board. The top plate
101
and the heater board
108
are adhered in a direction shown in
FIG. 6
to form oblong nozzles between nozzles
103
and the surface of the heater board
108
. In such adhering operation, the positions of both components are precisely adjusted in such a manner that a heater
109
is contained in each nozzle. Ink is supplied from an unrepresented ink tank, then guided to an ink liquid chamber
102
and reaches the interior of the nozzles
103
. The heater board
108
is controlled by an unrepresented control circuit and each heater
109
is energized according to the print data. The above-mentioned control circuit may be provided on the heater board or formed on another substrate, and will not be explained further as it is not related to the principle of the present invention.
The heater
109
energized according to the print data generates heat, thereby heating the ink in the corresponding nozzle. The heated ink boils above a certain critical temperature, thus generating a bubble. The generated bubble grows within a short time of several microseconds and gives an impact force to the ink, whereby a part of the ink is strongly pushed out and lands on a printing medium such as paper. A printed image is obtained by repeating this process.
In the following there will be explained the method of producing the top plate, with reference to
FIGS. 7A
to
7
H. In these drawings, the views at the right-hand side are those of the top plate
101
seen from the lower side (nozzle side) while those at the left-hand side are cross-sectional views of the top plate cut along a plane in the discharging direction.
FIG. 7A
illustrates a silicon wafer.
FIG. 7B
shows the formation of an oxide film.
FIG. 7C
shows patterning of SiO
2
.
FIG. 7D
shows formation of a SiN film.
FIG. 7E
shows the patterning of SiN.
FIG. 7F
shows anisotropic etching of Si, wherein a numeral
102
indicates a liquid chamber.
FIG. 7G
shows elimination of SiN.
FIG. 7H
shows anisotropic etching of Si, wherein a numeral
103
indicates a nozzle.
FIG. 7A
shows a silicon (Si) wafer
105
used as the material for forming the nozzle members, having a crystalline orientation <110> on the surface and <111> in the longitudinal direction of the nozzle. Both sides of the silicon wafer
105
are subjected to the formation of a thin silicon dioxide film
106
of a thickness of about 1 &mgr;m as shown in
FIG. 7B
, by thermal oxidation or CVD (chemical vapor deposition). The silicon dioxide layer
106
serves as a mask layer in anisotropic etching of silicon. Then, with the ordinary photolithographic process, the silicon dioxide layer
106
is patterned into the shape of nozzles and liquid chamber on one side (lower face in the illustration) and into the shape of the liquid chamber on the other side (FIG.
7
C). Then, on the nozzle forming side, a silicon nitride layer
107
is formed for example by CVD (
FIG. 7D
) and is patterned into the shape of the liquid chamber (FIG.
7
E).
The wafer is then subjected to anisotropic wet etching by immersion in etching liquid such as 22% solution of TMAH (tetramethylammonium hydride) whereby the etching proceeds in exposed areas of silicon on both sides of the wafer, namely according to the shape of the liquid chamber and the etched portions from both sides are eventually connected to form penetrating holes. Then the silicon nitride layer on the nozzle face is eliminated by etching (
FIG. 7G
) to expose the nozzle pattern formed in the silicon dioxide layer
106
in the step shown in
FIG. 7C
, and anisotropic etching is executed again with TMAH whereby a portion corresponding to the nozzle is etched. In this operation, the liquid chamber etched in the step shown in
FIG. 7F
is also further etched, but the shape of the liquid chamber is little affected because the etching time for the nozzle is shorter than that for the liquid chamber. Otherwise it is also possible to shorten the etching time for the liquid chamber in consideration of the etching time required for nozzle etching, thereby eventually obtaining the liquid chamber of the desired shape.
However, with the anisotropic etching of the present invention, there can be obtained a nozzle with a rectangular cross section because the <111> plane perpendicular to the wafer surface is present in the ink discharging direction, but, in the longitudinal direction of the nozzle, there is no crystalline plane capable of stopping the etching, so that the wall between the nozzles is overetched in the longitudinal direction to form an acute angle shape. Consequently, in such overetched portion, there inevitably remains the thin silicon dioxide film constituting the mask layer. Such silicon dioxide film alone is removed, without damaging silicon, by blowing pressurized air, eventually containing water, to the wafer. For removing the film of about 1 &mgr;m by blowing water with pressurized air, there is only required a pressure of 1 to 20 kgf/cm
2
. Otherwise the entire silicon dioxide film may be removed by wet etching employing the mixture of ammonium fluoride and hydrofluoric acid.
The top plate
108
prepared by the above-described process is shown in FIG.
8
. In the patterning process for forming the liquid chamber, the both surfaces of the top plate chip are formed in similar shapes, but the pattern at the ink supply side, at the upper surface in
FIG. 6
, may be made smaller at such a level that the penetrating hole is formed by anisotropic etching. In fact a pattern smaller than at the nozzle side is preferred in order to ensure the connection with the unrepresented ink supply member or the strength of the wafer in forming the top plate.
As explained in the foregoing, anisotropic etching of silicon can be utilized in forming the structure of the top plate, providing high mass producibility since the top plate can be prepared in the state of a wafer. Also the nozzle preparation by photolithographic technology allows to obtain nozzles of a high density with a high precision.
However, the conventional method of preparing the top plate has been associated with the following drawbacks because the nozzle walls and the liquid chamber frames are significantly different in width.
In forming the nozzles by adhering the top plate, principally comprising of silicon, with the heater board, the adhesion is most simply achieved by spraying an adhesive material. This is achieved by spraying, on the surface of the top plate, mist of a resinous adhesive material adjusted in viscosity with diluting liquid and mixed with compressed air. The adhesive comprises a material of high chemical resistance such as polyether amide resin (for example HIMAL supplied by Hitachi Chemical Co.), and is to form a protective film on the inner wall of the nozzle simultaneously with the coating of the adhesive material on the
Hiroki Tomoyuki
Ito Miki
Kashino Toshio
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Stephens Juanita
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