Etching a substrate: processes – Forming or treating thermal ink jet article
Reexamination Certificate
2002-06-27
2004-04-13
Alanko, Anita (Department: 1765)
Etching a substrate: processes
Forming or treating thermal ink jet article
Reexamination Certificate
active
06719913
ABSTRACT:
TECHNICAL FIELD
This invention relates to a printhead used in equipment for forming, through successive scanning operations, black and colour images on a print medium, usually though not exclusively a sheet of paper, by means of the thermal type ink jet technology, and in particular to the head actuating assembly and the associated manufacturing process.
BACKGROUND ART
Depicted in
FIG. 1
is an ink jet colour printer on which the main parts are labelled as follows: a fixed structure
41
, a scanning carriage
42
, an encoder
44
and, by way of example, printheads
40
which may be either monochromatic or colour, and variable in number.
The printer may be a stand-alone product, or be part of a photocopier, of a “plotter”, of a facsimile machine, of a machine for the reproduction of photographs and the like. The printing is effected on a physical medium
46
, normally consisting of a sheet of paper, or a sheet of plastic, fabric or similar.
Also shown in
FIG. 1
are the axes of reference:
x axis: horizontal, i.e. parallel to the scanning direction of the carriage
42
; y axis: vertical, i.e. parallel to the direction of motion of the medium
46
during the line feed function; z axis: perpendicular to the x and y axes, i.e. substantially parallel to the direction of emission of the droplets of ink.
The composition and general mode of operation of a printhead according to the thermal type technology, and of the “top-shooter” type in particular, i.e. those that emit the ink droplets in a direction perpendicular to the actuating assembly, are already widely known in the sector art, and will not therefore be discussed in detail herein, this description instead dwelling more fully on some only of the features of the heads and the manufacturing process, of relevance for the purposes of understanding this invention.
The current technological trend in ink jet printheads is to produce a large number of nozzles per head (≧300), a definition of more than 600 dpi (dpi=“dots per inch”), a high working frequency (≧10 kHz) and smaller droplets (≦10 pl) than those produced in earlier technologies.
Requirements such as these are especially important in colour printhead manufacture and make it necessary to produce actuators and hydraulic circuits of increasingly smaller dimensions, greater levels of precision, narrow assembly tolerances. It is important in particular to ensure that the volume and speed of the droplets subsequently emitted are as constant as possible, and that no “satellite” droplets are formed as these, with a trajectory generally different from the main droplets, are distributed randomly near the edges of the graphic symbols, reducing their sharpness.
FIG. 2
shows an enlarged axonometric view of an actuating assembly
111
of an ink jet printhead according to the known art, made of a die
100
of semiconductor material (usually Silicon), on the upper face of which resistors
27
have been made for emission of the droplets of ink, driving circuits
62
for driving the resistors
27
, soldering pads
77
for connecting the head to an electronic controller not shown in the figure, and which bears a pass-through slot
102
through which the ink flows from a reservoir not shown in the figure. Around the upper edge of the slot
102
a basin
76
has been made, the characteristics and functions of which are as described in detail in Italian patent application TO 98A 000562. Affixed to the upper face of the die is a layer
105
of photopolymer having, usually though not exclusively, a thickness less than or equal to 25 &mgr;m in which, by means of known photolithographic techniques, a plurality of ducts
53
and a plurality of chambers
57
positioned locally to the resistors
27
have been made. Stuck on the photopolymer
105
is a nozzle plate
106
, generally made of a plate of gold-plated nickel or kapton, of thickness less than or equal to 50 &mgr;m, bearing a plurality of nozzles
56
, each nozzle
56
being in correspondence with a chamber
57
. In the current technology, the nozzles
56
have a diameter D of between 10 and 60 &mgr;m, while their centres are usually spaced apart by a pitch A of {fraction (1/300)}
th
or {fraction (1/600)}
th
of an inch (84.6 &mgr;m or 42.3 &mgr;m). Generally, though not always, the nozzles
56
are arranged in two rows parallel to the y axis, staggered one from the other by a distance B=A/2, in order to double the resolution of the image in the direction parallel to the y axis; the resolution thus becomes {fraction (1/600)}
th
or {fraction (1/1200)}
th
of an inch (42.3 &mgr;m or 21.2 &mgr;m). The x, y and z axes, already defined in
FIG. 1
, are also shown in FIG.
2
.
FIG. 3
is an axonometric enlargement of two chambers
57
, adjacent and communicating with the slot
102
through the basin
76
and the ducts
53
made in the layer of photopolymer
105
. Normally the ducts
53
have a length l and a rectangular cross-section having a depth a and a width b. The chambers
57
have a depth d, substantially equal to the depth a of the ducts
53
.
A section of an ejector
55
can be seen in
FIG. 4
, where the following are shown, in addition to the items already mentioned: a reservoir
103
containing ink
142
, a droplet
51
of ink, a vapour bubble
65
, a meniscus
54
in correspondence with the surface of separation between the ink and the air, an external edge
66
and arrows
52
which indicate the prevalent direction of motion of the ink.
To describe the operation of an ejector for a thermal type ink jet printhead, an electrical analogy is used, for which the following equivalences are established:
V = electrical voltage in volt
equivalent to: pressure in N/m
2
;
I = current in A
equivalent to: flow rate m
3
/s;
R = resistance in ohm
equivalent to: hydraulic resistance in
N/m
2
/m
3
/s = N s/m
5
;
L = Inductance in henry
equivalent to the ratio between the mass of
the column of liquid that fills the duct and
the square of the section of the duct; this
ratio is called “hydraulic inertance”, and
is measured in kg/m
4
;
C = capacitance in farad
equivalent to: hydraulic compliance
in m
3
/N/m
2
= m
5
/N.
In the equivalent diagram of
FIG. 5
the bubble is represented as a variable capacitance C
b
. There is a front leg
70
, equivalent to the whole formed by the chamber
57
, the nozzle
56
, the meniscus
54
and the droplet
51
, and a rear leg
71
, which represents the section of the hydraulic circuit between the chamber
57
and the reservoir
103
.
The front leg
70
comprises a fixed impedance L
f
, R
f
corresponding substantially to the chamber
57
, a variable impedance L
u
, R
u
corresponding substantially to the nozzle
56
, and a deviator T which, during the step in which the droplet
51
is formed, inserts a variable resistance R
g
substantially corresponding to the droplet, whereas, during the steps of withdrawal of the meniscus
54
, of filling of the nozzle, of subsequent oscillation and damping of the meniscus, inserts a capacitance C
m
substantially corresponding to the meniscus itself.
Ejection of the ink takes places in accordance with the following steps:
a) The electronic control circuit
62
supplies energy to the resistor
27
, so as to produce local boiling of the ink with formation of the bubble
65
of steam in expansion. During this step, in the equivalent electric circuit of
FIG. 5
the variable resistance R
g
is inserted. The bubble
65
generates two opposing flows: I
p
(to the reservoir
103
) and I
a
(to the nozzle
56
).
b) The electronic circuit
62
terminates the delivery of energy to the resistor
27
, the vapour condenses, the bubble
65
collapses, the droplet
51
detaches itself, the meniscus
54
withdraws emptying the nozzle
56
. The two opposing flows I
p
and I
a
remain. In this step, in the equivalent circuit of
FIG. 5
the capacitance C
m
corresponding to the meniscus
54
is inserted.
c) The bubble
65
has disappeared, the meniscus
54
demonstrates its capillarity and goes back towards the outer edge
66
Conta Renato
Scardovi Alessandro
Alanko Anita
Banner & Witcoff , Ltd.
Olivetti Tecnost S.p.A.
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