Low expansion snout insert for inkjet print cartridge

Details Low expansion snout insert for inkjet print cartridge Low expansion snout insert for inkjet print cartridge

1999-05-26

2001-02-13

Le, N. (Department: 2861)

Incremental printing of symbolic information

Ink jet

Fluid or fluid source handling means

Reexamination Certificate

active

06186622

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to inkjet printers and, in particular, to an improvement in inkjet print cartridges.
BACKGROUND
A complete description of an inkjet printer and an inkjet print cartridge is provided in U.S. Pat. No. 5,648,806, entitled “Stable Substrate Structure For A Wide Swath Nozzle Array In A High Resolution Inkjet Printer,” by Steven Steinfield et al., assigned to the present assignee and incorporated herein by reference. In inkjet print cartridges, poor print and image quality can be caused by misplaced ink drops, referred to as dot placement error or DPE. A main contributor to DPE is nozzle camber angle (NCA) caused by warpage of the tape automated bonded (TAB) head assembly. The TAB head assembly is a strip of flexible tape having nozzles formed therein and conductors formed on its back surface. A printhead substrate is secured to the back of the tape, and electrodes on the substrate are connected to the conductors on the tape. Contact pads on the cartridge receive electrical signals from the printer to eject ink drops from the nozzles.
The tape is secured to the snout of the print cartridge, and a fluid seal is made between the tape and the body of the print cartridge to allow ink to be fed around the edges of the substrate (or through a hole in the substrate) in order to reach ink ejection chambers formed on the top of the substrate. An ink ejection element in each ink ejection chamber is energized to eject a droplet of ink through an associated nozzle located over each ink ejection chamber.
A great deal of the flexible tape warpage may be created during the assembly process of securing the TAB head assembly to the print cartridge body.
Besides warpage affecting the nozzle angles, other undesireable effects caused by non-flatness of the TAB head assembly include die edge camber angle and macrodimple. These defects affect print quality, print speed, reliability, and serviceability. The table below summarizes the different components of the TAB head assembly flatness and their effects on customer perceivable attributes of the end product.
The flatness component of
causes
affecting
NCA
Drop trajectory
print quality
(Nozzle camber angle)
variation
throughput:
(directionality)
(# of
printmode
passes
required)
DECA
Drop volume and drop
print quality
(Die edge camber angle)
velocity variation
DECA
Firing chamber refill
print speed
(Die edge camber angle)
frequency
variation/reduction
Buckling (a.k.a.
Wiping and capping
serviceability
“macrodimple”)/Warp (a.k.a.
margin reduction
“ripple”)
Buckling (a.k.a.
Delamination stress, ink
reliability
“macrodimple”)/Warp (a.k.a.
shorts robustness
“ripple”)
degradation
FIG. 1
is a perspective view of an inkjet print cartridge
10
, and
FIG. 2
is a cross-sectional view of the printhead portion of the print cartridge of
FIG. 1
along line
2
—
2
. The components in the above table are identified in FIG.
2
.
Generally, print cartridge
10
of
FIG. 1
includes a print cartridge body
12
, having a snout
14
, which typically faces downwards toward a medium when the cartridge is installed in a scanning carriage. A printhead area
16
includes a nozzle member
18
having nozzles
20
formed therein. Nozzle member
18
may be formed of a flexible tape
22
(FIG.
2
), as described above, or may be any other thin material.
Below nozzle member
18
is a printhead substrate
24
(FIG.
2
), typically formed of silicon, having formed on it ink ejection elements, an ink ejection chamber surrounding each ink ejection element, and ink channels leading to the ink ejection chambers. Details are described in U.S. Pat. No. 5,648,806.
FIG. 2
is a cross-section along line
2
—
2
of
FIG. 1
illustrating one type of printhead using a TAB head assembly. The plastic print cartridge body
12
supports the edges of the TAB head assembly. A substrate
24
is shown attached to the underside of the flexible tape
22
. Ink flows from a reservoir in the print cartridge body
12
(or from an external reservoir) through an ink channel
25
in the print cartridge and into ink channels formed in a barrier layer on the surface of the substrate
24
. The flexible tape
22
is sealed with respect to the print cartridge by an adhesive
26
. Energizing signals are coupled to copper traces
28
formed on the back of the flexible tape
22
to energize the ink ejection elements to eject droplets of ink from the nozzles
20
formed in the flexible tape
22
. A cover layer
30
prevents ink from contacting the copper traces
28
.
As seen from
FIG. 2
, the flexible tape
22
is warped, which results in the effects previously described. One cause of the warpage is due to the thermal cycling of the print cartridge during manufacturing. The coefficients of thermal expansion of the print cartridge body
12
and the flexible tape
22
are not the same, causing the two components to expand to different extents when being heated, such as during heat curing of the adhesive
26
. When these components are later cooled to room temperature, the fixing of the tape
22
to the print cartridge body
12
by the adhesive
26
causes compression of the tape
22
and distortion.
What is needed is a technique for improving the flatness of the TAB head assembly or any other nozzle member assembly.
SUMMARY
Described herein is a snout insert which is pressed fit into the snout of a plastic print cartridge. The snout insert (referred to herein as an expander) has a low coefficient of thermal expansion (CTE) and a high tensile modulus relative to the print cartridge body. The expander is designed for a precise fit into the snout and, in one embodiment, includes machinable datums to ensure a tight fit.
In one embodiment, the expander is inserted through the ink reservoir area in the print cartridge body and pushed into the snout, rather than being inserted through the opening at the top of the snout where the printhead substrate is placed.
The press fit forces the snout into an expansion beyond the point to which it would ordinarily expand during the thermal cure cycle. The result is that, during the thermal cure cycle, the snout only changes as a function of the expander's CTE. The expander then remains in the print cartridge throughout its life.
The CTE of the plastic print cartridge body along the short axis of the snout may exceed 100 ppm/° C., and the CTE of the flexible tape is approximately 17 ppm/° C. The expander must narrow this gap to prevent significant warpage of the tape. Hence, the CTE of the expander should, ideally, be low enough to reduce the resulting CTE of the snout to approximately the CTE of the tape, or less than the CTE of the tape. Additional detail regarding the CTE of print cartridge material is found in U.S. Pat. No. 5,537,133, entitled Restraining Element For A Print Cartridge Body To Reduce Thermally Induced Stress, by Jaren Marler et al., assigned to the present assignee and incorporated herein by reference.
The expander can be formed of a molded low CTE material or a low CTE metal.


REFERENCES:
patent: 5506608 (1996-04-01), Marler et al.
patent: 5537133 (1996-07-01), Marler et al.
patent: 5648806 (1997-07-01), Steinfield et al.

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