Patent Application
20080152821
The following description relates to ink jet printing. Ink jet printing allows for precise deposition of material onto a substrate. Referring to
A printing system is described that has a fluid emitter and a conductive plate. The fluid emitter is configured to emit droplets into a printing region on a substrate. The conductive plate is for supporting the substrate onto which the droplets are emitted, wherein the conductive plate is uniformly conductive within the printing region.
A system for printing onto a substrate is described. The system includes a printhead, a chuck for supporting a substrate on which the printhead is configured to deposit fluid and a conductive lead configured to be connected to a conductive portion of the substrate.
A method of printing onto a substrate is described. The method includes connecting a conductive portion of the substrate to ground, to a resistor or to a bias and printing onto the substrate.
The methods and systems described herein can include one or more of the following features. The conductive plate may be grounded or may be connected to a bias source. The conductive plate may have a uniform thickness within the printing region. The conductive plate may be free of recesses or holes within the printing region or be free from protruding features in the printing region. The conductive plate may be formed of metal, carbon loaded plastic, ElectroStatic Dissipative plastic or porous sintered metal. The conductive plate may be a conductive chuck that supports the substrate. A system may further comprise a chuck for supporting the substrate and the conductive plate is a conductive pad that is supported by the chuck or a vacuum apparatus in fluid communication with the conductive plate to hold the substrate fixedly in place. A system can include a conductive lead connected to a resistor. Printing the droplets can include printing onto an insulating substrate, an oxide or glass or plastic. Printing the droplets can include printing organic fluid, biological material or polymer, such as a polymer dissolved in a carrier vehicle. Printing onto a substrate can include forming a conductive layer on the substrate. Forming the conductive layer can include depositing a layer of carbon on the substrate or depositing a layer of metal on the substrate. The conductive portion of a substrate can be carbon, such as carbon black, or a layer of anti-static spray. The substrate may be a non-conductive porous substrate, such as a non-conductive porous plastic, rubber foam, adsorbent polyethylene fiber pad or ceramic. The printing system can include a drop watcher for recording drops that are formed and released from the printhead.
Potential advantages of the techniques described herein include being able to reduce the electrical voltage potential present on the surface of an insulating substrate. Charged droplets can be applied more accurately onto the substrate when the substrate's surface voltage, and hence the electrical field present between printhead nozzle and substrate surface is reduced. Smaller droplets, which are more easily deflected by an electric field, can be more accurately applied to an insulating substrate. When high precision printing onto an insulating substrate is required, such as in jetting biological fluids and forming high resolution displays using jetting to apply the display pixels, the conductive backing can allow for the accuracy in droplet deposition that is required. A dropwatcher on system can be used to set up printing of a new substance or fluid. Watching the formation of the droplets allows for modification to the waveform used to form the droplets and therefore can fine tune the printing process.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring to
Referring to
The chuck 120 has uniform conductivity within the printing area. In some embodiments, the chuck 120 is as large as or has a perimeter that is greater than the perimeter of the substrate 20. If the chuck 120 extends at least to the edges of the substrate that is being printed on or beyond the edge of the substrate, areas of charge build-up are avoided on the substrate. In some embodiments, the chuck is free from areas of non-uniformity, such as holes, slots, recesses, raised features or changes in material, which can allow for regions of higher field strength to form on the substrate.
The chuck 120 is formed of a conductive material, such as a metal, carbon loaded plastic, electrostatic dissipative (ESD) plastic, that is, a plastic material with a resistivity in the range of 109 Ohm*cm or less, or other suitable material. In some embodiments, the chuck is formed of a flat plate of porous sintered metal, which allows an integral substrate hold-down function through the use of an applied vacuum through the thickness of the metal. The chuck 120 is electrically connected to earth or circuit ground, either directly or through a component in the printing system 100, such as the circuitry that drives the printhead. To electrically ground the chuck, a conductive lead can be attached to the chuck, such as by direct contact, soldering or by forming a hole in the chuck and wrapping wire through the hole. The wire is then attached to ground. Alternatively, a fastener, such as a rivet or a screw is driven into the chuck and holds the wire in place on the chuck. In some embodiments, the chuck is slightly biased to a potential rather than being connected to ground. In some embodiments, the chuck is connected to a large-valued resistor. The chuck ground wire can be connected to the drive circuitry ground for the printer 5 or to a related earth ground.
Referring to
Whether a conductive pad or a conductive chuck is used, the substrate is in contact with the conductive material during printing. As the printing system 100 applies droplets onto the substrate, the substrate is moved relative to the nozzle. Even as the substrate moves, the chuck, or pad, is kept under the substrate in the printing area.
In some embodiments, a conductive layer is applied directly to the back side of the substrate, such as by sputtering or using a conductive paint or adhesive. The conductive layer is then grounded during printing. Optionally, the conductive layer can be removed once the printing process is complete.
Some types of substrates are particularly susceptible to charge buildup during printing. Porous substrates, for example, which are able to absorb the liquid components of the liquid printing fluid, formed of non-conductive materials can build up a charge. Porous plastic, such as plastic sheets available from Porex® in Fairburn, Ga., and porous ceramics are substrates that can develop a net charge and repel drops jetted onto the substrate.
Solutions for printing onto porous substrates can include applying a conductive layer onto the porous substrate prior to printing. One exemplary method of printing onto a porous substrate includes depositing a layer of carbon onto the porous substrate to enhance conductivity of the substrate. In some substrates, carbon black is mixed into plastic prior to molding the plastic. The plastic can be any type of thermoplastic, such as polypropylene or polyethylene. Alternatively, or in addition, a conductive layer is applied to the porous substrate, such as by sputtering a layer of metal onto the substrate. The conductive layer can be removed after printing, if desired. Another method of printing onto a porous substrate includes selecting a conductive porous substrate, such as a sintered carbon or sintered nickel substrate, for example, parts made from stainless steel, bronze, nickel, nickel based alloys, titanium, copper, aluminum or precious metals, such as porous metal parts available from Mott Corporation, Farminton, Conn. As with the conductive backing, the conductive material is connected to a ground or is slightly biased to drain off charge. Yet another solution is to apply an anti-static spray, such as StatFree Spray, available from PerfectData® in Norristown, Pa., to the substrate to dissipate charge. The spray forms a layer of slightly conductive anti-static material on the substrate. Alternatively, if the ink is conductive, the ink can be used to provide a path to a ground connection.
Referring to
While the conductive layer, chuck or pad, conductive backing for short, is able to reduce the electrical field that is formed on the substrate, it may not entirely eliminate the electric field. The conductive backing effectively increases the capacitance presented to the charge on the surface of the substrate. The magnitude of the charge formed upon ejection of the fluid droplets is more or less constant regardless of the presence of the conductive backing. Thus, the same amount of charge is delivered to the substrate during printing, and accumulated on its surface, with or without the conductive backing in place. Thus, by increasing the capacitance presented to the charge the electric field between the substrate and the printhead nozzle is also greatly reduced, compared to when there is no conductive backing. The difference between printing on an insulating substrate with and without a conductive backing can be a factor between 2-1000 or more. The effect of reducing the electric field on the surface of the substrate is that when a charged droplet approaches the surface of the substrate, the reduced electric field creates proportionately less deflection of the charged droplet than would a higher electric field. The droplet is able to land in the desired position without being significantly affected by the deposited surface charge, as shown in
To enable using any of the conductive backings, layers or substrates described herein, a printing system can optionally include a conductive lead that can be connected to the conductive element. The lead is electrically conductive and connected to either ground, a relatively large resistor, that is, a resistor with a resistance greater than a mega-ohm, or a voltage source, such as a small DC or AC voltage source. The lead can include a wire, a conductive adhesive, a fastener, such as an alligator clip, or other element that enables the lead to be fastened, either temporarily or permanently, to the conductive element.
A printing system with the conductive plate or conductive chuck described herein is capable of reducing electric field build up on an insulating substrate, even in low humidity or low oxygen environments. This can be advantageous when the droplets or the substrate must be kept in an environment that is free from water or oxygen. Such droplets can be water or oxygen sensitive organic materials, such as electrically conductive polymers, biological materials, desiccating materials, DNA precursors or other such sensitive materials. Accurate droplet placement can be more critical in applications where very small droplets are required, such as to form high resolution displays or to test biological samples where only a very minute amount of sample is applied. As drops get smaller, the absolute amount of charge per drop generated is larger, so the critical quantity, that is, the charge to mass ratio, is much larger. Smaller droplets in the range of 0.1 to 20 picoliters are more prone to being forced away from a desired printing location by an electric field on a substrate than larger droplets. Larger droplets are often better able to resist the force from the electric field because of their greater droplet mass relative to the droplet's ejection-induced charge potential, and are less likely to stray from their trajectory.
The conductive backing can be useful in a number of applications, such as printing liquid crystal color filter material onto glass to form LCD display components, forming plasma displays or backplanes, or printing biological samples or DNA precursors onto a glass substrate or slide. Printing into or onto a grounded conductive porous substrate or a porous substrate having a grounded conductive layer thereon can be useful when multiple droplets are being jetted at the same location. The systems and techniques described herein can also be used to set up a printer for printing a new material. For example, in a system having a drop watcher 180, as described in U.S. Publication No. 2007/0013736, droplets can be repeatedly printed onto a substrate 20 to determine the shape of the droplet and to optimize the waveform used to jet the droplets, as shown in
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
All references described herein are incorporated by reference for all purposes.
This application claims priority to U.S. Provisional Application Ser. No. 60/871,868, filed on Dec. 26, 2006. The disclosure of the prior application is considered part of and is incorporated by reference in the disclosure of this application.
| Number | Date | Country | |
|---|---|---|---|
| 60871868 | Dec 2006 | US |
