Process for reducing blockage in nozzle holes for ink jet...

Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means

Reexamination Certificate

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Reexamination Certificate

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06179417

ABSTRACT:

TECHNICAL FIELD
The present invention is directed to ink jet printing. In particular, it is directed to a process for reducing blockage in nozzle holes by a prior treatment of the foam ink reservoir.
BACKGROUND OF THE INVENTION
In commercial manufacture of cartridges for ink jet printing, a number of the cartridges have been returned to the factory from the field as failures. The predominant mode of failure was that no ink came out of the cartridge at what was supposed to be the beginning of its life in use. The present invention provides a solution to blockage in nozzle holes of ink jet print heads.
DISCLOSURE OF THE INVENTION
It has now been discovered that the failure of ink to come out of the cartridges is due to blockage of the printhead's nozzle holes, and that this blockage is avoided by treating the polyether polyurethane foam pads which are often employed/found in the ink reservoir(s) of inkjet cartridges.
According to the present invention, the polyether polyurethane foam is treated by immersing it in cold de-ionized water for a period of at least six hours. The immersion can continue for up to about 72 hours, after which there is little reason to continue it any longer.
The immersion of the polyether polyurethane foam in water resulted in the removal of oily material which was identified as low molecular weight urethanes. We have also identified low molecular weight urethanes as the material blocking the holes in the nozzles.
It is believed that the foam contains residual materials from its manufacture, i. e., materials that are unreacted and materials which do not reach complete reaction or are a product of degradation in the foam manufacturing process. These materials are leached out by the water based ink and, with time, migrate to the nozzle plate causing nozzle blockage.
Most surprisingly, the water used in the present invention is preferably cold. Warm water, and even water at ordinary room temperature, do not work as well as cold water. The most preferred temperature for the water is 4° C., where the results are by far the most desired. The reason for this is not understood.
Treatment of the foam according to the present invention in no way harms the final results obtained. The treated foam of this invention was tested in production level print cartridges and the production level print cartridges having treated foam performed comparable to functional print cartridges having untreated foam. The testing included such parametric measurements as drop mass, drop velocity, drop rise time, flooding, life test and print quality.


REFERENCES:
patent: 4794409 (1988-12-01), Cowger et al.
patent: 4824487 (1989-04-01), Hefferman
patent: 4929969 (1990-05-01), Morris
patent: 4931811 (1990-06-01), Cowger et al.
patent: 5128379 (1992-07-01), Stone
patent: 5182579 (1993-01-01), Haruta et al.
patent: 5387379 (1995-02-01), Atarashi et al.
“Hawley's Condensed Chemical Dictionary” Revised by Richard J. Lewis, Jr; p. 353, 1993.

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