Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Patent
1993-09-13
1995-10-31
Fuller, Benjamin R.
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
347 94, 347 95, G01D 1518
Patent
active
054634164
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to pulsed droplet deposition apparatus and more particularly to a method of operating such apparatus having a droplet liquid chamber, a nozzle communicating with said chamber for expulsion of droplets of said liquid therethrough, droplet liquid replenishment means connected with said chamber and energy pulse applying means for imparting pulses of energy to the droplet liquid in the chamber to effect droplet ejection from said nozzle. One familiar form of apparatus of the kind set forth is the drop-on-demand ink jet printer which would normally take the form of a plurality or an array of parallel ink channels having respective nozzles communicating therewith and ink replenishment means connecting the respective channels with a common ink supply.
Such drop-on-demand printers, which eject drops of fluid ink asynchronously in response to piezo-electrically or electro-thermally induced energy pulses, are known. The inks for the printers are selected to form a printed dot having high optical density and controlled spreading characteristics on the printing surface, which is typically uncoated or plain paper.
The inks which satisfy these print requirements consist typically of a solvent and ink solids including colorants, such as dyes or pigments, and possibly other additives. The ink solids may attain as much as 10-15% by weight of the ink composition and also tend to cause the ink viscosity to be enhanced substantially above that of the ink solvent alone.
When the ink viscosity is increased, the viscous impedance to flow of ink in the nozzle during pulsed drop ejection is increased, so that a higher input energy pulse is required to effect drop ejection. Accordingly it is desirable to limit ink viscosity in order to limit the operating energy or voltage. This is desirable because higher voltage requires a more expensive drive circuit or chip and, therefore, increases the manufacturing and operating cost and also reduces the reliability of the printer.
SUMMARY OF THE INVENTION
The present invention consists in the method of operating pulsed droplet deposition apparatus, of the kind referred to, which is characterised by applying said pulses to droplet liquid in said chamber having a relatively low viscosity at high shear rate and a relatively high viscosity at low shear rate, said liquid having a relaxation time constant of the same order or greater than the period of pulses applied thereto and having a characteristic time in said nozzle of the same order or less than the period of said pulses.
The liquid viscosity which controls the viscous impedance in the nozzle, is the viscosity at the shear rate obtaining in the nozzle which is, in the case of an ink jet printer ink, typically in the range 10.sup.5 -10.sup.7 sec.sup.-1. It has been found that an ink, preferably a visco-elastic ink, having a step viscosity characteristic providing viscosity which is high at low shear rate and low at high shear rate can be employed according to the present invention so that it possesses relatively low viscosity during the period of the imparted energy pulse at the end of which the viscosity is tending to increase. The viscous impedance to flow in the nozzle is thus reduced so that the quantity of ink delivered for a given magnitude of pressure pulse is increased.
Preferably, the energy pulse imparting means comprises electrically operated means for displacing a part of a side wall of said chamber. One such electrically operated means comprises a piezo-electrically actuated chamber side wall. The use of a displaceable chamber side wall is to be preferred to an electro-thermal pulse generator which produces a vapour bubble in the droplet liquid because the energy transduction to the liquid is more efficient and there are fewer constraints on the ingredients and properties of the droplet liquid employed.
In alternative forms, the method of the invention is employed to operate a printer having either a plurality of or an array of ink channels having respective nozzles communic
REFERENCES:
patent: 4290072 (1981-09-01), Mansukhani
patent: 5112398 (1992-05-01), Kruse
Kruse Jurgen M.
Paton Anthony D.
Fuller Benjamin R.
Lund Valerie Ann
XAAR Limited
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