Surfactant for inkjet service station wiper fluid

Details Surfactant for inkjet service station wiper fluid Surfactant for inkjet service station wiper fluid

2000-04-19

2002-04-30

Le, Nancy (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S033000

Reexamination Certificate

active

06378981

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a service station wiper fluid in an inkjet ink printing system, which in addition to a servicing solvent, also has a surfactant which together with the solvent will be called the servicing fluid in this invention. The servicing fluid improves the consistent wetability of the nozzle plate, thus stabilizing the drop directionality of the ink from inkjet nozzle to the print media.
BACKGROUND OF INVENTION
The use of inkjet printing systems has grown dramatically in recent years. This growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Today's inkjet printers offer acceptable print quality for many commercial, business, and household applications at costs fully an order of magnitude lower than comparable products available just a few years ago. Notwithstanding their recent success, intensive research and development efforts continue toward improving inkjet print quality, while further lowering cost to the consumer.
An inkjet image is formed when a precise pattern of dots is ejected from a drop-generating device known as a “printhead” onto a printing medium. The typical inkjet printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an inkjet printhead substrate. The substrate incorporates an array of firing chambers that receive liquid ink (colorants dissolved or dispersed in a solvent) through fluid communication with one or more ink reservoirs. Each chamber has a thin-film resistor, known as a “firing resistor,” located opposite the nozzle so ink can collect between the firing resistor and the nozzle. In particular, each resistor element, which is typically a pad of a resistive material, measures about 35 &mgr;m×35 &mgr;m. The printhead is held and protected by an outer packaging referred to as a print cartridge, i.e., inkjet pen.
Upon energizing of a particular resistor element, a droplet of ink is expelled through the nozzle toward the print medium, whether paper, transparent film or the like. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements, thereby forming alphanumeric and other characters on the print medium.
Inkjet printers generally have a printhead service station to which an inkjet printhead is moved by the carriage, and a cap which sealingly contacts the printhead is generally located at the service station. At the service station, the printhead (or multiple heads if such are used) are occasionally cleaned and, if necessary, primed with ink. For use in this cleaning function, wipers are located at the service station. The service station can include a “sled” carrying these elements and others required to service the one or more printheads of the printer. This sled itself can be moved transversely to an axis of motion of the printhead carriage, for example in a vertical direction, so as to bring the caps or wipers into or out of contact with the printhead. Alternatively, a tumbler can be provided at the service station, and wipers, as well as caps, can be located on the tumbler. Rotation (and in some cases also vertical movement) of the tumbler effects wiping of the printhead, and/or alignment of one or more caps with one or more printheads positioned adjacent the tumbler at the service station.
To improve printing speed and the clarity and contrast of the printed image, recent advancements in the art have focused on improving the ink itself. For example, to provide faster, more waterfast printing with darker blacks and more vivid colors, improved pigment-based inks for inkjet applications have been developed. These pigment-based inks have a higher suspended solids content than earlier dye-based inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. However, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, in this case not only from the dried ink and minute dust particles or paper fibers, but also from the solids within the inks themselves. Further, this ink is more difficult to remove when dried than previously used dye-based inks. These characteristics compound the problems affecting print quality mentioned above.
Another characteristic of these pigment-based inks contributes to the nozzle clogging problem. The pigment-based inks use a dispersant to keep the pigment particles from flocculating. Unfortunately, the dispersant tends to form a tough film on the printhead orifice plate face. This dispersant film attracts and binds paper dust and other contaminants as well as solids from the ink itself. It has been recognized that this film, as well as ink residue and debris surrounding the printhead nozzles, is quite difficult to remove from the printhead.
It has been recognized that application of a servicing solvent will help mitigate the problem of dried ink by slowing the drying of ink or redissolving ink residue, rendering the printhead more easily cleanable by wiping. However problems associated with use of a servicing solvent have been identified.
Storage of the servicing solvent in adequate amounts for the life of the printer without leaking is problematic. For example leaks can occur caused by the tipping of the printer. Also, pressure differentials can occur because of a change in temperature or altitude during shipment. Also when treatment fluid is applied to a printhead, it is hard to avoid contaminating the source of servicing solvent by undesirable accumulations of ink solids, dispersants, and other debris. It is therefore desirable to maintain the means of applying servicing solvent and the servicing solvent itself in an uncontaminated state to provide consistent printhead cleaning over the life of the printer.
Also, it is important to meteri the amount of servicing solvent applied in wiping. Consistent optimal cleaning effectiveness as well as print quality can be compromised by application of too little or too much servicing solvent. Too little servicing solvent results in less effective residue removal allowing undesirable accumulation. Too much servicing solvent can result in one or more nozzles being at least temporarily disabled due to excess servicing solvent being pushed into the nozzle by the wiper, or drawn into the nozzle by negative pressure associated with operation.
With the constant need to apply and wipe off servicing solvent on the nozzle plate surface in order to keep it clean, the wetability of the surface is affected. This in turn affects the drop directionality of the ink as it is directed from the inkjet nozzles. The need exists for a way to stabilize the wetability of the nozzle plate surface so that the drop directionality of the ink directed from the inkjet nozzles can be stabilized to shoot consistently straight drops onto the print media.
With the existing technology, the nozzle plate has inconsistent wetting or surface energy during the life of the printhead. This causes the amount of ink left on the nozzle plate after wiping to change during the life of the print head.
The present inventors have found that adding a compatible surfactant to the servicing fluid controls the wetability of the nozzle plate during the life of the printhead.
SUMMARY OF THE INVENTION
The present invention relates to a system for servicing a portion of an inkjet printer having a printhead, comprising: a servicing fluid reservoir; a printhead wiper; means for releasing a predetermined amount of servicing fluid from said reservoirs onto said wiper; a wiper scraper; means for sequentially moving said wiper from a first location where said wiper engages said means for releasing to receive said predetermined amount of servicing fluid to a second location remote from said first location and said means for releasing, where said wiper engages said printhead to transfer said predetermined amount of said servicing fluid onto and wipe unwanted accumulations from said printhead,

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