Method for improving drop charging assembly flatness to improved drop charge uniformity in planar electrode structures

An improved continuous ink jet print station includes a drop generator with a jet array and a drop charging assembly. The drop charging assembly includes a substrate with a first side facing the jet array, and one or more resistive heater elements placed on the substrate aligned with the jet array. The resistive heater elements are discontinuously disposed on portions of the substrate. One or more one charging electrodes are disposed on the first side. The continuous ink jet print station includes a power source for powering the resistive heater elements to heat the substrate to a temperature sufficient to prevent condensation of fluid on the first side.

FIELD OF THE INVENTION

The present embodiments relate to methods for providing an improved drop charging assembly for a print station. Better drop control is realized by increasing the uniformity of the charge on catch drops and reducing the variation of the charge on print drops that typically cause poor print quality

BACKGROUND OF THE INVENTION

In continuous ink jet printing, electrically conductive ink is supplied under pressure to a region that distributes the ink via a plurality of orifices, typically arranged in a linear array. The ink discharges from the orifices, forming a jet array, which breaks into droplet streams. Individual ink droplets in the droplet streams are selectively charged by a drop charging assembly, which deflects the drops from their normal trajectories. The deflected drops may be caught and recirculated. The undeflected drops are allowed to proceed to a print medium forming an image.

Drops are typically charged by a drop charging assembly having a plurality of charging electrodes along one edge, and a corresponding plurality of connecting leads along one of the faces. The edge of the drop charging assembly, having charging electrodes, is placed in close proximity to the ink droplet stream. Charges are applied to the leads to induce charges in the drops as they break off from the jet array.

Uniformity of drop charge is essential in continuous ink jet printheads utilizing planar electrode structures. These printheads require a substantial difference in charge for the “catch drops” compared to the “print drops”. Drops with a high charge are attracted towards a catcher and recycled. Drops with a low charge are printed on print media. Print quality defects are introduced if the charge on the print drops is excessive or uncontrolled. Nominal charge level on the print drops varies in each printhead design.

Pipkorn U.S. Pat. No. 4,622,562 teaches that a charge plate for a printhead must be heated to prevent the formation of condensate, see also, Wood U.S. Pat. No. 4,928,116. The prior art described herein are incorporated by reference.

A need exists to improve print quality with a better drop charging assembly, in particular, for print stations with arrays longer than 4 inches.

The present embodiments described herein were designed to meet these needs.

SUMMARY OF THE INVENTION

The continuous ink jet print station includes a fluid system that provides fluid to a drop generator. The drop generator has a jet array, a midpoint, and a catcher assembly opposite the jet array to return fluid to the fluid system. The print station includes a drop charging assembly disposed opposite the jet array for charging drops from fluid projected from the jet array.

The drop charging assembly has a substrate with a first side facing the jet array with a first side surface area. The assembly has multiple resistive heater elements placed on the substrate aligned with the jet array. The multiple resistive heater elements are discontinuously disposed on portions of the substrate. The assembly has one or more charging electrodes disposed on the first side in communication with drop charging electronics and a power source to provide voltage to the resistive heater elements to heat the substrate to a temperature sufficient to prevent condensation of fluid on the first side while minimizing distortion of the first side.

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular descriptions and that it can be practiced or carried out in various ways.

The improved drop charging assembly for an ink jet print station has discontinuous, resistive heater elements that minimize condensation on the drop charging assembly while creating a uniform charge on the “catch drops” and “print drops” of the print station.

The improved drop charging assembly provides better manufacturing yields, better printhead reliability, and better print quality, particularly for drop generators with orifice plates with small orifices.

The improved drop charging assembly is particularly valuable with long arrays of jets in printheads, which have a tendency to otherwise deform while heating with other types of heating elements. The improved drop charging assembly results in lower energy needed to remove condensate formed on the drop charging assembly.

This improved drop charging assembly enables the printhead to be maintained more easily than other printheads. One embodiment describes a design that includes making a multilayer resistive heater element directly on the substrate of the drop charging assembly, thereby lowering manufacturing costs when compared to other processes that require separate heater elements to be manufactured and assembled on the drop charging assembly.

With reference to the figures,FIG. 1depicts an overall design of a continuous ink jet print station with the improved drop charging assembly. The continuous ink jet print station includes a drop generator12with a jet array14for projecting ink droplets15, and a drop charging assembly16. A catcher assembly17is disposed opposite the jet array14. The drop charging assembly16includes a substrate18having a first side20facing the jet array14. A fluid system40supplies ink or other fluids to the drop generator12. An example of an ink jet print station is a Kodak Versamark DT92 print station available from Kodak Versamark of Dayton, Ohio.

The substrate18has a second side21that has a common edge with the first side20. The second side21has a surface area greater than the first side20surface area. The substrate18has a third side23having a common edge with the first side20opposite the common edge of the second side21. The third side23surface area is greater than the first side20surface area.

At least one charging electrode24is disposed on the first side20and at least one resistive heater element22ais disposed on the third side23.

Drop charging electronics25connect to the charging electrode24. A power source26connects to the resistive heater element22a. One power source26can power each resistive heater element, but it is possible to have one power source26that supplies voltages to all the resistive heater elements disposed on the substrate18.

In a preferred embodiment, the drop charging assembly16includes at least one resistive heater element22aon the substrate18extending parallel to the jet array14, but discontinuously disposed on selected portions of the substrate18. The resistive heater element22is shown in segments inFIG. 2. At least six resistive heater elements22a,22b,22c,22d,22e, and22fare preferably disposed on the substrate18for an exemplary printhead using 300 orifices per inch. The three important sides of the substrate,20,21and23, are shown inFIG. 2. The resistive heater elements are shown on second side of the substrate21.

In this embodiment, the six resistive heater elements are shown in a preferred embodiment paired together, and disposed symmetrically around the midpoint42of the jet array.

FIG. 3shows another embodiment of the resistive heater element on the third side23of the substrate, which is the side opposite21of the substrate18. The jet is shown in this embodiment. The charging electrode24is disposed on the first side of the substrate20that connects to drop charging electronics25by way of conductors43disposed on the second side21.

The charging electrode is typically disposed on the first side in the most preferred embodiment. Any method for forming electrodes or circuit traces on a substrate can be used to form the charging electrodes. Particular processes described by Morris in U.S. Pat. No. 5,512,117, are preferred methods and incorporated herein.

The resistive heater element can be formed by using sequential thick film deposition processes, such as screen printing and firing between layers, directly on the substrate.

The resistive heater elements can be printed or created as a group, saving time over labor intensive resistor build, and adheres to techniques that have existed.

The resistive heater elements can be used as a circuit layer34to form the leads to the resistive elements, for instance, a DuPont 6160 from E.I. DuPont of Wilmington, Del. An example of a resistive layer36used to form the heaters is a DuPont Q587 resistor. As for the dielectric coating layer38to protect both the circuit layer and the resistive layer, a DuPont 9615 dielectric material can be used.

In the most preferred embodiment, multiple resistive heater elements are placed on the substrate on a side different from the first side but aligned with the jet array and in proximate relation to the first side.

In another embodiment, the resistive heater element can be formed on a non-conductive polymer sheet, such as a polyimide, that is laminated to the substrate. In another embodiment, the resistive heater element can be formed using vacuum depositing, sputtering, evaporation, and vapor deposition of the layers onto the substrate. If sputtering is performed, the substrate is placed in a vacuum chamber, plasma is generated in a passive source gas in the chamber, and ion bombardment is directed toward the substrate, causing material to be sputtered off the target and condensed on the substrate. For evaporation, the substrate is placed in a high vacuum chamber at room temperature with a crucible containing the material to be deposited. A heating source is used to heat the crucible, causing the material to evaporate and condense on the substrate. Finally, low pressure chemical vapor deposition is performed in a reactor at temperatures up to 900° C. The deposited film is a product of a chemical reaction between the source gases supplied to the reactor.

Each resistive heater element has a separate power source26. For example, a PS1-01-687, a 24 volt DC power supply can be used, which is available from VICOR of Sunnyvale, Calif.

FIG. 5shows six resistive heater elements22a,22b,22c,22d,22eand22f, each with a power source26a,26b,26c,26d,26e, and26frespectively. The power sources could be the VICOR part described above.

The drop charging assembly can further include at least one charging electrode24disposed on the first side20. The drop charging electrode24shown inFIG. 1preferably has a bent configuration around the substrate18.

The continuous ink jet print station includes a power source26for powering the resistive heater element to heat the substrate to a temperature sufficient to prevent condensation of fluid on the first side, as shown inFIG. 1. The power source26can comprise a pulse width modulated power source that varies the power to the discrete heater elements This power source can vary the on time relative to the off time within a defined period to modify the total power supply to a resistive element. Typically the defined period is 1000 microseconds with an on time of 300 microseconds.

Alternatively, the power source26can vary the voltage supplied to the discrete heater elements.

The embodiments have been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the embodiments, especially to those skilled in the art.

PARTS LIST

12. drop generator14. jet array15. ink droplets16. drop charging assembly17. catcher assembly18. substrate20. first side of substrate21. second side of substrate22a. first resistive heater element22b. second resistive heater element22c. third resistive heater element22d. fourth resistive heater element22e. fifth resistive heater element22f. sixth resistive heater element23. third side of substrate24. charging electrode25. drop charging electronics26. power source34. circuit layer36. resistor layer38. dielectric coating layer40. fluid system to provide fluid to a drop generator42. jet array a midpoint43. conductors