Abstract:
A printer for digital printing in which ink is deposited in metered amounts on a substrate. The printer includes a wheel rotatable by a shaft of a motor, an idler disposed in a paint reservoir, and a segment of wire disposed around the wheel and the idler. A computer controls movement of the wire by controlling the rotation of the wheel. As the motor rotates the wheel, ink contained within the paint reservoir coats the wire and is drawn by the wire in front of an air stream, which pulls the ink from the wire and carries it toward the substrate. The wire has alternatively hydrophilic and hydrophobic areas, causing the ink to form droplets on the wire for printing them as discrete pixels onto the substrate.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is related and claims priority to U.S. Provisional Patent Application Ser. No. 60/764506, filed Feb. 2, 2006, which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     Two conventional printing techniques include ink jet printing and screen printing. Ink jet printers work by depositing small droplets of ink in various colors, typically cyan, magenta, yellow and black, on a print medium or substrate to form a color image. Conventional thermal ink jet printing heads include several nozzles and thermal elements. Ink is expelled from the nozzles in a jet by bubble pressure created by heating the ink using the thermal elements while the nozzles and thermal elements are in close proximity. Ink jet print heads use relatively small orifices, valves, and nozzles for depositing the desired quantity and color of ink on the print medium. Therefore, very fine grade inks are required in which particle sizes of the pigments within the inks are kept to a minimum to help keep the orifices, valves, and nozzles of the ink system from becoming clogged.  
         [0003]     In screen printing, ink is forced through a design-bearing screen onto the substrate being printed. The screen is made of a piece of porous, finely woven fabric stretched over a wood or aluminum frame. Areas of the screen are blocked off with a non-permeable material, a stencil, which is a negative of the image to be printed. The screen is placed on top of a piece of print substrate, often paper or fabric. Ink is placed on top of the screen, and scraper blade is used to push the ink evenly into the screen openings and onto the substrate. The ink passes through the open spaces in the screen onto the print substrate; then the screen is lifted away. The screen can be re-used for multiple copies of the image, and cleaned for later use. If more than one color is being printed on the same surface, the ink is allowed to dry and then the process is repeated with another screen and different color of ink. Screen printing requires use of inks having a relatively high viscosity to prevent all the ink from simply passing through the screen onto the print substrate.  
         [0004]     Accordingly, a need exists for an improved apparatus and method for printing inks.  
       SUMMARY  
       [0005]     A method, consistent with the present invention, can be used to form a pattern on a substrate. The method includes coating at least a portion of an exterior surface of a cable with alternating hydrophilic and hydrophobic areas, coating at least a portion of the exterior surface of the cable with an ink, directing an air stream at the portion of the cable coated with the ink, and electronically controlling advancement and position of the cable through the air stream such that a metered amount of the ink is removed from the exterior surface of the cable and is deposited onto the substrate to form a pattern on the substrate.  
         [0006]     An apparatus, consistent with the present invention, can deposit an ink on a substrate. The apparatus includes an electronically controllable drive mechanism and a structure associated with the drive mechanism and movable thereby. At least a portion of an exterior surface of the structure has alternating hydrophilic and hydrophobic areas. An ink supply is in communication with the structure for depositing ink on at least a portion of the structure. At least one fluid nozzle having at least one nozzle orifice is positioned and oriented for directing at least one jet of fluid toward at least a portion of the structure to remove an amount of the ink from the structure and direct the amount toward a substrate. The movement of the structure relative to the at least one fluid nozzle substantially controls the amount of the ink removed from the structure, and the amount of the ink directed to the substrate form a pattern on the substrate.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings,  
         [0008]      FIG. 1  is a perspective view of one embodiment of a fluid delivery system or printer;  
         [0009]      FIG. 2  is a side view of the fluid delivery system of  FIG. 1 ;  
         [0010]      FIG. 3  is a diagram of a system to use the printer to print materials onto a substrate;  
         [0011]      FIG. 4  is a diagram illustrating a first type of ink flow when a print wire is not moving;  
         [0012]      FIG. 5  is a diagram illustrating a second type of ink flow when a print wire is not moving;  
         [0013]      FIG. 6  is a diagram illustrating a print wire having alternating hydrophilic and hydrophobic areas; and  
         [0014]      FIG. 7  is a diagram illustrating the alternating hydrophilic and hydrophobic areas forming droplets on the print wire. 
     
    
     DETAILED DESCRIPTION  
     Printing System  
       [0015]      FIG. 1  is a perspective view of one embodiment of the fluid delivery system or printer, generally indicated at  10 .  FIG. 2  is a side view of the fluid delivery system or printer of  FIG. 1 . A pulley  13  having a circumscribing groove  38  defined therein is secured to a shaft  15  of a motor  14 . An elongate frame member  32  is secured to frame or plate  12  and extends into a reservoir of ink  24 . A rotatable or stationary guide  34  is attached to a distal end  37  of elongate frame member  32 . Guide  34  is illustrated as a cylindrical, non-rotatable member having a groove  40  circumscribing guide  34  in which a wire cable  36  can slide during rotation of wheel  13 . Alternatively, guide  34  can be implemented with a rotatable member. As used herein, the term “cable” or “wire” or “wire cable” or “elongate segment” is meant to include the use of a wire, a cable formed of multiple wires, a rod, a saw tooth wheel, or variations thereof. Wire cable  36  is disposed in groove  38  circumscribing the wheel  13  and in groove  40  circumscribing guide  34 .  
         [0016]     An elongate reservoir retaining member  16  is attached to plate  12  and includes a flange  18  defining a notch  20  between the flange  18  and elongate reservoir retaining member  16 . Notch  20  is configured to receive a top lip  22  of ink reservoir  24 . A bottom plate  26  is secured to a distal end  28  of elongate reservoir retaining member  16  with a threaded nut  31  that is threaded onto a threaded shaft  33 . Threaded shaft  33  is secured to distal end  28  of elongate reservoir retaining member  16 . Bottom plate  26  abuts against the bottom  30  of ink reservoir  24  and holds it between flange  18  and bottom plate  26 .  
         [0017]     An air supply hose  42  is secured to a nozzle body  44  and supplies air through a nozzle orifice  46  that is aimed at a portion of cable  36 . A cable guide  48  defining a longitudinal slot  50  is positioned proximate nozzle orifice  46 . Cable  36  rides within slot  50  and is thus held in relative position to nozzle orifice  46  so that air passing therethrough does not substantially move cable  36  from in front of nozzle orifice  46  or cause cable  36  to substantially vibrate. Slot  50  can alternatively include a small rotatable guide.  
         [0018]     Rotation of shaft  15  may be controlled by a controller, generally indicated at  57 . Any type of controller may be used. In one embodiment, the controller includes circuitry  54  in a module  56  that receives signals from a signal generating device  52 , such as a microprocessor or other devices that can supply discrete signals to instruct selective rotation of the shaft  15  of the motor. Circuitry  54  receives a signal(s) from generating device  52  and rotates shaft  15  of the motor according to the signal(s).  
         [0019]     In operation, ink contained in reservoir  24  is picked up by wire cable  36  and advanced by rotation of wheel  13 , indicated by the arrow, in front of nozzle orifice  46 . Fluid that is blown through nozzle orifice  46  disperses or pulls the ink from cable  36  toward the print medium. Depending on the viscosity of the ink in the reservoir, the cross-sectional diameter of cable  36 , and the diameter of wheel  13 , a relatively precise amount of ink can be dispensed. The ink is dispersed onto a substrate  58 , as illustrated in  FIG. 2 .  
         [0020]     The print head in system  10  can include alternative implementations, as shown in FIG. 1A in U.S. Pat. No. 5,944,893 and described in the corresponding text. For example, the print head can include a discontinuous wire, guide  34  can be rotatable, a spring tensioning mechanism can be used, and an air solenoid can be used to turn the air supply on and off.  
         [0021]     The fluid delivery system or printer of the present invention is based on printer technology that is described in U.S. Pat. Nos. 5,944,893; 5,972,111; 6,089,160; 6,090,445; 6,190,454; 6,319,555; 6,398,869; and 6,786,971, all of which are incorporated herein by reference.  
         [0022]     As used herein, the term “ink” is meant to include any pigmented material, including, but not limited to, inks, dyes, paints, particle loaded suspensions, or other similarly pigmented liquids.  
         [0023]     As used herein, the term “print medium” or “substrate” are meant to include any print medium known in the art, including but not limited to paper, plastic, polymer, synthetic paper, non-woven materials, cloth, metal foil, vinyl, films, glass, wood, cement, and combinations or variations thereof. The print medium or substrate can be a rigid material or a flexible material.  
         [0024]      FIG. 3  is a diagram of a system  130  to use the printer to print ink onto a substrate. System  130  includes a print head  148  mounted on a track  142  supported by vertical posts  144  and  146 , a wall, or other support. Print head  148  corresponds with printing system  10 . A drive unit  134 , using a motor, controls movement of print head  148  along track  142  in an x-direction as indicated by arrows  140 . A substrate support  150  is located on a track  136 , which would be supported by a vertical post, wall, or other support. A drive unit  132 , using a motor, controls movement of substrate support  150  along track  136  in a y-direction as indicated by arrows  138 . A substrate can be mounted or otherwise affixed to substrate support  150 , and a line or pattern can be printed upon the substrate by print head  148 . The configuration of the line or pattern is determined by the coordinated movement of print head  148  along track  142  and the substrate on substrate support  150  along track  136 .  
         [0025]     A computer  100 , corresponding with controller  57  and used to implement controller  57 , electronically controls print head  148  and drive units  132  and  134  for moving substrate support  150  and print head  148 , respectively. Computer  100  can include, for example, the following components: a memory  112  storing one or more applications  114 ; a secondary storage  120  for providing non-volatile storage of information; an input device  116  for entering information or commands into computer  100 ; a processor  122  for executing applications stored in memory  112  or secondary storage  120 , or as received from another source; an output device  118  for outputting information, such as information provided in hard copy or audio form; and a display device  124  for displaying information in visual or audiovisual form. Computer  100  can optionally include a connection to a network such as the Internet, an intranet, or other type of network.  
         [0026]     Computer  100  can be programmed to control movement of print head  148  along track  142  and substrate support  150  along track  136 . In particular, computer  100  can be programmed to electronically control movement of print head  148 , via drive unit  134 , in x-direction  140  laterally across a substrate on substrate support  150 , and computer  100  can be programmed to electronically control movement of the substrate on substrate support  150 , via drive unit  132 , in y-direction  138  vertically with respect to print head  148 . Computer  100  also controls print head  148 , as described above, for movement of the wire and delivery of the ink from the wire to the substrate. Computer  100  can also be programmed to control an air solenoid in system  10 . The use of tracks  136  and  142  for coordinated movement of substrate support  150  and print head  148 , respectively, thus effectively functions as an X-Y stage for using the printer to print a wide variety of shapes and configurations of patterns, lines, or other elements. As an alternative, lines or patterns can be printed using one of the following techniques: coordinated movement of print head  148  in the y-direction and substrate support  150  in the x-direction; movement of print head  148  in both the x-direction and y-direction; or movement of substrate support  150  in both the x-direction and y-direction.  
         [0027]     Computer  100  can also be programmed to control the printer for radial printing. In particular, a first orifice can direct an air jet at the wheel or wire to remove paint in a purely radial direction, while other orifices supplying air can be angled above the air jet created by the first orifice to help eliminate conical divergence of the paint as it is pulled from the surfaces of the wheel or wire.  
       Use of Hydrophilic and Hydrophobic Areas on the Print Wire  
       [0028]     As described above, the printer uses a wire to carry ink from the ink reservoir to the air jet, which blows the ink off the wire and onto the surface being coated. The quantity and quality of ink applied to the surface depends on the wire feed rate, rheologic properties of the ink, air flow, orifice geometry, and distance from the print head to the surface, among other things. The mechanism for this ink transport is shown in  FIGS. 1 and 2 .  FIG. 3  illustrates an exemplary system for printing a line or pattern on a substrate using the printer.  
         [0029]     The printing system tends to provide overspray of the ink, which can be undesirable for certain uses of the system in that the overspay may provide ink where it is not required. When a pixel is meant to be printed, the wire is forwarded to pull the ink out of the doctor blades and in front of the orifice. When the system is to stop printing, the wire is stopped. The air flows out of the orifice at all times during the printing process, the main effect of which produces most of the overspray on a printed line by ink moving on the wire. Simply stopping the wire does not stop the ink from moving in front of the orifice. This effect is due to either the ink trickling back down from the wire above the orifice due to gravity, or the ink getting pulled out of the doctor blades back up the wire due to the venturi effect and cohesion of the ink.  
         [0030]     These effects are shown in  FIGS. 4 and 5 . As shown in  FIG. 4 , an orifice  162  provides an air spray  164  across a wire  160 . When wire  160  stops moving, ink flow  166  and  168  occurs down the wire and into air spray  164  due to gravity. As shown in  FIG. 5 , an orifice  172  provides an air spray  174  across a wire  170 , and doctor blades  180  and  182  are positioned adjacent wire  170 . When wire  170  stops moving, ink flow  176  and  178  occurs upward from doctor blades  180  and  182  into air spray  174  due to the venturi effect.  
         [0031]     One method to eliminate this potentially undesirable effect involves using alternate stripes of hydrophilic areas  192  and hydrophobic areas  194  on a wire  190 , as shown in  FIG. 6 . The ink  196  sticks only to the hydrophilic part of the wire, creating droplets, as shown in  FIG. 7 . The droplets can then be blown from the wire with the air jet, creating a discrete volume pixel. The hydrophobic areas  194  also act to block the flow of ink up and down the wire  190  when it is not moving. This feature can improve print quality by reducing overspray and quantizing the ink on the wire. Depending upon the type of ink used, it may adhere to either the hydrophilic or hydrophobic areas of the wire. For example, a water-based ink will adhere to the hydrophilic areas, and a solvent-based ink will adhere to the hydrophobic areas.  
         [0032]     The wire can be coated or otherwise treated in order to create the hydrophilic and hydrophobic areas. Examples of such coatings include the following: diamond-like glass (DLG); diamond-like carbon (DLC); fluoropolymers; polymers; and silanes. Example of such treatments include the following: etching; a plasma treatment; and a corona treatment. The hydrophilic areas on the wire can alternatively comprise bare sections of the wire without any coating. Examples of materials used to create hydrophobic and hydrophilic regions on the surface of an article are described in U.S. Pat. No. 6,352,758, which is incorporated herein by reference. Examples of plasma treatment and corona treatment are described in, respectively, U.S. Pat. Nos. 5,888,594 and 5,939,182, both of which are incorporated herein by reference.  
         [0033]     DLG is an amorphous carbon system including a substantial quantity of silicon and oxygen that exhibits diamond-like properties. In these films, on a hydrogen-free basis, there is at least 30% carbon, a substantial amount of silicon (typically at least 25%) and no more than 45% oxygen. DLC is an amorphous film or coating comprising approximately 50 to 90 atomic percent carbon and approximately 10 to 50 atomic percent hydrogen, with a gram atom density of between approximately 0.20 and approximately 0.28 gram atoms per cubic centimeter, and composed of approximately 50% to approximately 90% tetrahedral bonds.  
         [0034]     The use of DLC, or alternatively DLG, is desirable to create a durable surface energy differential. It is desirable to create a very durable surface on the membrane of a wire jet print head. This durable surface would allow the print head to be cleaned occasionally by wiping the head across a squeegee-type element to remove surface materials. It is possible to deposit a thin uniform layer of DLC on a polymer substrate. If the polymer substrate is part of the print head, the outside surface of the nozzle membrane would have the DLC on it at the end of manufacturing. DLC is a very low surface energy material, making it extremely difficult for a fluid to wet out and remain on that surface. This feature would make it difficult for an wire jet ink to cause adverse or undesirable effects in the print head. In addition, DLC is a very durable surface, allowing a user to wipe the surface clean from time to time. The long term stability and usability of the print heads would be improved by this coating.  
         [0035]     DLG and DLC are described in U.S. patent application Ser. No. 11/185,078, filed Jul. 20, 2005, which is incorporated herein by reference.  
       EXAMPLE  
       [0036]     The print head used to print ink for the example refers to a print head consistent with the print head in the printer described above. The term “standoff” used in the example describes the distance between the wire on the print head and the print medium. The term “air pressure” refers to the regulated air pressure applied to the orifice block. The term “shim thickness” refers to the size of the shim placed between the two halves of the doctor blade. The shim determines the gap between the edges of the doctor blade and the wire. The terms “paint velocity”, “paint acceleration”, and “paint deceleration” refer to the velocity, acceleration, and deceleration parameters of the program controlling the motor. The orifice design OP-001 refers to a three-hole orifice in a substantially equilateral triangular configuration in which a center hole at the top point of the triangular shape has a diameter of 0.023 inches and the lower holes at the bottom two points of the triangular shape each have a diameter of 0.02 inches.  
         [0037]     Alternating hydrophilic and hydrophobic areas were formed on a print wire in the printer. The hydrophobic areas consisted of TSS 8881 acrylic screen print ink (available from 3M Company, St. Paul, Minn.) applied to the wire. The ink was diluted in methyl ethyl ketone, then applied to the wire in regular intervals with a cotton swab. The hydrophobic areas were approximately 0.5 centimeter (cm) long, with approximately 1 cm gaps between areas. The hydrophilic areas comprised the bare wire, the 1 cm gaps, without any coating.  
         [0038]     Water with green food coloring was applied to the wire and was observed adhering only to the hydrophilic part of the wire, creating droplets. The droplets were then blown from the wire onto a paper substrate with the air jet, creating a discrete volume pixel. Discrete spots of the green water droplets from the wire were observed on the paper substrate. Table 1 provides the coating parameters for this example.  
                             TABLE 1                           Coating Parameters                Coating Parameter   Data                       Work type   Functionalized wire           Paint formulation   Green food coloring and water           Viscosity   Unknown           Substrate   Paper           Air pressure   10 psi           Standoff (can to substrate)   0.25 inches           Wire diameter   0.008 inches           Shim thickness   0.010 inches           Orifice design   OP-001           Paint velocity   6.28 inches/second (in/s)           Paint acceleration   62.8 in/s 2             Paint deceleration   62.8 in/s 2             Wire multiple   Wire feed = 3.14 in/s           Number of passes   1