Patent Application
20110310144
1. Field of the Invention
The present invention relates generally to inkjet printing and specifically to the use of dielectric heating within an inkjet nozzle to expel a drop of ink.
2. Related Art
Inkjet printers work by squirting ink onto paper. They are non-impact printers in the sense that there is no physical contact between the paper and the print head to render images on a sheet of paper (or other medium). Unlike other non-impact printers, such as laser printers, inkjet printers use aqueous ink to create the images on the paper.
A typical inkjet print head comprises a plurality of nozzles which can simultaneously impart ink from the nozzle to the paper. Presently, the two major types of nozzles in widespread use are thermal nozzles and piezoelectric nozzles.
The performance of the thermal nozzle is constrained by the ability of the nozzle to dissipate heat from a heating element contained in the nozzle to heat the ink. Because the heating element is electrically and thermally coupled to the substrate controlling the nozzle, heat must be dissipated from the substrate. Overheating can lead to damage to the print head and controlling circuitry. The issue of heat dissipation limits the speed of printing, the density of nozzles and the number of nozzles that can simultaneously fire. Because not all nozzles can fire simultaneously, multiple passes must be made when high density color is required such as in photo quality printing.
Piezoelectric nozzles require complex waveforms to “wiggle” drops out of the nozzle requiring greater complexity and size to the print head control circuits. Furthermore, most piezoelectric crystals included in piezoelectric nozzles operate at higher voltages than standard control circuitry.
A novel inkjet delivery system, method and device are disclosed. A print head system comprises an ink reservoir, a nozzle and conductive plates. An alternating current signal at microwave frequencies produces an electric field between the conductive plates and across the ink reservoir. This causes explosive nucleation which causes a bubble in the ink to form which expels a drop of ink from the nozzle. In one embodiment, the conductive plates are thermally insulated from the ink reservoir. In another embodiment, electrolytes are added to the ink to improve the dielectric heating in the ink. In another embodiment, the walls of the ink reservoir can comprise texturing or projections to roughen the surface lowering the energy needed for nucleation.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
A detailed description of embodiments of the present invention is presented below. While the disclosure will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the disclosure.
It should be noted that the conductive plates are shown as parallel conductive plates: other configurations can be used. However, parallel conductive plates are among the simplest. Additionally, the plates are shown here as inside the wall of the ink reservoir, but can easily be outside as shown later. The size of the dielectric nozzle can dictate the spacing of the plates. For example, a typical thermal inkjet nozzle has a reservoir on the order of 10 microns. Therefore, the conductive plates may be placed 10 microns apart.
The circuitry to drive an alternating current between 1 GHz and 20 GHz can be found in various modern wireless technologies. For example, 802.11 WiFi standards use 2.4 GHz and 5 GHz for transmissions. In fact, there are numerous ways to generate a signal in the 1 GHz to 20 GHz range, including circuitry comprising complementary metal-oxide-semiconductor (CMOS) technology. Furthermore, since the purpose of the signal generator is to heat the ink, the frequency supplied to the conductive plates does not need to be of a specific frequency as they would for a signal used for communications. Hence some design constraints, such as the precise frequency of operation placed on the signal generator, can be relaxed. However, regulatory considerations may dictate the frequency selection. For example, microwave ovens operate at 2.45 GHz because the Federal Communications Commission (FCC) has allocated that frequency for microwave ovens to prevent interference with other communications. In this situation, the choice of frequencies may be limited for regulatory concerns but not for operational considerations.
The heating process works because of the polar nature of the water in the ink. Therefore, the energy transfer to the water can be improved by ionizing the water further. This can be accomplished by the addition of electrolytes, such as a salt, to the water. A small amount of electrolyte can increase the ionization in the water but without any effect on the quality of the image printed. The increase in ionization leads to more efficient transfer of energy from the alternating current to the water.
Nucleation is known to take place at lower energies when containers have rough edges rather than a smooth container. As a result, the addition of texturing or projections can lower the energy and temperature required for a bubble to form.
Furthermore, texturing can be applied to the walls of the ink reservoir even with projections.
An array of dielectric nozzles described above can be used in a printer head in an inkjet printer. Because, the amount of heat to be dissipated is less than that of a thermal nozzle, more nozzles can eject ink simultaneously resulting in fewer passes of the printer head for applications like photo quality printing.
Furthermore, inkjet printing can be used for other applications, such as fabrication. For example, inkjet printing can be used in fabricating electrical or optical device, particularly for deposing organic materials such as organic dyes. In addition, inkjet printing technology has been used to create organic transistors, conducting polymers, structural polymers, ceramics, nanoparticles, metals, nucleic acids, and protein arrays. Inkjet printing has even been used to deposit DNA onto membranes. Other researchers have used inkjet printing to print antigens onto polycarbonate materials for immunoassay. Still others have used inkjet printing to fabricate small biosensors. One researcher has even used inkjet printing to “print” human liver cells onto a buffer.
It should be emphasized that the above-described embodiments are merely examples of possible implementations. Many variations and modifications may be made to the above-described embodiments without departing from the principles of the present disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
