Patent Publication Number: US-6905201-B2

Title: Solid phase change ink melter assembly and phase change ink image producing machine having same

Description:
RELATED CASE 
     This application is related to U.S. application Ser. No. 10/320,854 entitled “HIGH SHEAR BALL CHECK VALVE DEVICE AND A LIQUID INK IMAGE PRODUCING MACHINE USING SAME”; and U.S. application Ser. No. 10/320,820 entitled “PHASE CHANGE INK MELTING AND CONTROL APPARATUS AND METHOD AND A PHASE CHANGE INK IMAGE PRODUCING MACHINE HAVING SAME”; and U.S. application Ser. No. 10/320,853 entitled “SOLID PHASE CHANGE INK PRE-MELTER ASSEMBLY AND A PHASE CHANGE INK IMAGE PRODUCING MACHINE HAVING SAME”, each of which is being filed herewith on the same day and having at least one common inventor. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to image producing machines, and more particularly to a solid phase change ink melter assembly and a phase change ink image producing machine or printer having same. 
     In general, phase change ink image producing machines or printers employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops. 
     An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 5,372,852 issued Dec. 13, 1994 to Titterington et al. As disclosed therein, the phase change ink printing process includes raising the temperature of a solid form of the phase change ink so as to melt it and form a molten liquid phase change ink. It also includes applying droplets of the phase change ink in a liquid form onto an imaging surface in a pattern using a device such as an ink jet printhead. The process then includes solidifying the phase change ink droplets on the imaging surface, transferring them the image receiving substrate, and fixing the phase change ink to the substrate. 
     Conventionally, the solid form of the phase change is a “stick”, “block”, “bar” or “pellet” as disclosed for example in U.S. Pat. No. 4,636,803 (rectangular block 24, cylindrical block); U.S. Pat. No. 4,739,339 (cylindrical block); U.S. Pat. No. 5,038,157 (hexagonal bar); U.S. Pat. No. 6,053,608 (tapered lock with a stepped configuration). Further examples of such solid forms are also disclosed in design patents such as U.S. Pat. No. D453,787 issued Feb. 19, 2002. In use, each such block form “stick”, “block”, “bar” or “pellet” is fed into a heated melting device that melts or phase changes the “stick”, “block”, “bar” or “pellet” directly into a print head reservoir for printing as described above. 
     Conventionally, phase change ink image producing machines or printers, particularly color image producing such machines or printers, are considered to be low throughput, typically producing at a rate of less than 30 prints per minute (PPM). The throughput rate (PPM) of each phase change ink image producing machine or printer employing solid phase change inks in such “stick”, “block”, “bar” or “pellet” forms is directly dependent on how quickly such a “stick”, “block”, “bar” or “pellet” form can be melted down into a liquid. The quality of the images produced depends on such a melting rate, and on the types and functions of other subsystems employed to treat and control the phase change ink as solid and liquid, the imaging member and its surface, the printheads, and the image receiving substrates. 
     There is therefore a need for a relatively high-speed (greater than “XX” PPM) phase change ink image producing machine or printer that is also capable of producing relatively high quality images, particularly color images on plain paper substrates. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a solid phase change ink melter assembly is provided in a phase change ink image producing machine. The solid phase change ink melter assembly includes (a) a melter housing having walls defining a melting chamber; and (b) a positive temperature coefficient (PTC) heating device mounted within the melting chamber for heating and melting solid pieces of phase change ink into melted molten liquid ink 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the invention presented below, reference is made to the drawings, in which: 
         FIG. 1  is a vertical schematic of the high-speed phase change ink image producing machine or printer including the solid phase change ink melter assembly of the present invention; 
         FIG. 2  is a partially exploded perspective view of the melting and control system including the solid phase change ink melter assembly of the present invention; 
         FIG. 3  is a perspective, partially exploded view of the solid phase change ink melter assembly  FIG. 2 ; and 
         FIG. 4  is a perspective illustration of the PTC heater of the solid phase change ink melter assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     Referring now to  FIG. 1 , there is illustrated an image producing machine, such as the high-speed phase change ink image producing machine or printer  10  of the present invention. As illustrated, the machine  10  includes a frame  11  to which are mounted directly or indirectly all its operating subsystems and components, as will be described below. To start, the high-speed phase change ink image producing machine or printer  10  includes an imaging member  12  that is shown in the form of a drum, but can equally be in the form of a supported endless belt. The imaging member  12  has an imaging surface  14  that is movable in the direction  16 , and on which phase change ink images are formed. 
     The high-speed phase change ink image producing machine or printer  10  also includes a phase change ink delivery subsystem  20  that has at least one source  22  of one color phase change ink in solid form. Since the phase change ink image producing machine or printer  10  is a multicolor image producing machine, the ink delivery system  20  includes four (4) sources  22 ,  24 ,  26 ,  28 , representing four (4) different colors CYMK (cyan, yellow, magenta, black) of phase change inks. The phase change ink delivery system also includes the melting and control apparatus ( FIG. 2 ) for melting or phase changing the solid form of the phase change ink into a liquid form, and then supplying the liquid form to a printhead system  30  including at least one printhead assembly  32 . Since the phase change ink image producing machine or printer  10  is a high-speed, or high throughput, multicolor image producing machine, the printhead system includes four (4) separate printhead assemblies  32 ,  34 ,  36  and  38  as shown. 
     As further shown, the phase change ink image producing machine or printer  10  includes a substrate supply and handling system  40 . The substrate supply and handling system  40  for example may include substrate supply sources  42 ,  44 ,  46 ,  48 , of which supply source  48  for example is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets for example. The substrate supply and handling system  40  in any case includes a substrate handling and treatment system  50  that has a substrate pre-heater  52 , substrate and image heater  54 , and a fusing device  60 . The phase change ink image producing machine or printer  10  as shown may also include an original document feeder  70  that has a document holding tray  72 , document sheet feeding and retrieval devices  74 , and a document exposure and scanning system  76 . 
     Operation and control of the various subsystems, components and functions of the machine or printer  10  are performed with the aid of a controller or electronic subsystem (ESS)  80 . The ESS or controller  80  for example is a self-contained, dedicated mini-computer having a central processor unit (CPU)  82 , electronic storage  84 , and a display or user interface (Ul)  86 . The ESS or controller  80  for example includes sensor input and control means  88  as well as a pixel placement and control means  89 . In addition the CPU  82  reads, captures, prepares and manages the image data flow between image input sources such as the scanning system  76 , or an online or a work station connection  90 , and the printhead assemblies  32 ,  34 ,  36 ,  38 . As such, the ESS or controller  80  is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the machine&#39;s printing operations. 
     In operation, image data for an image to be produced is sent to the controller  80  from either the scanning system  76  or via the online or work station connection  90  for processing and output to the printhead assemblies  32 ,  34 ,  36 ,  38 . Additionally, the controller determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface  86 , and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface  14  thus forming desired images per such image data, and receiving substrates are supplied by anyone of the sources  42 ,  44 ,  46 ,  48  and handled by means  50  in timed registration with image formation on the surface  14 . Finally, the image is transferred within the transfer nip  92 , from the surface  14  onto the receiving substrate for subsequent fusing at fusing device  60 . 
     Referring now to  FIGS. 1-4 , the melter assembly  300  of the present invention is further illustrated in greater detail. As shown, each color ink CYMK (represented by the letters A, B, C, D) has a melter assembly  300 , and description of one will suffice as a description of each of the others. Each melter assembly  300  includes a housing  302  that has walls  304  defining a melting chamber  306 . Each melter assembly  300  also includes a positive temperature coefficient (PTC) heating device  310  that is mounted within the melting chamber  306  for heating and melting solid pieces of phase change ink to turn them into melted molten liquid ink. Each melter housing  302  also includes an electrically insulative member  312  between the PTC heating device  310  and a base  308  of the melter housing. Each housing  302  further includes a screen device  314  that is mounted below the PTC heating device  310  as shown for removing unwanted particles from the melted molten liquid ink coming from the heating device  310 . 
     The PTC heating device  310  is comprised of a device frame  316  made of a conductive material such as aluminum, a pill portion  320 , and a folded fin  322 ,  324  that is also made of a conductive material such as aluminum. The folded fin  322 ,  324  acts as a heating element for providing the heat and melting surface area that contact and melt the solid pieces phase change ink. As shown, the PTC heating device includes a pair  322 ,  324  of the folded fins, with one mounted to each side of the pill portion  320 . The pill portion  320  is formed and set for self-regulating or controlling the PTC heating device  310  at a control temperature Tc of about 170° C. which is calculated to be significantly higher than a melting temperature Tm (110° C.) of the solid phase change ink. The pill portion  320  is made for example of strontium titanate, and is of the open loop type, meaning that its performance is affected by the material temperature Tw of the solid pieces of phase change ink being heated. 
     In general, PTC heaters function as self-regulating heating elements. They can operate at a nearly constant temperature over a broad range of voltage and current dissipation conditions. PTC heaters as such can be manufactured in many different shapes such as discs, rectangles, squares, cylinders, and various other shapes, and each shape can include holes or passages for increasing heating surface area. 
     As shown in  FIGS. 3-4 , the PTC heating device  310  of the present invention includes a pair of electrodes  326 ,  328  that are connected to the folded fins  322 ,  324 . In addition, each folded fin  322 ,  324  defines through-passages or channels  330 , which are located between each pair of fin folds  332  for example. The folded aluminum fins  322 ,  324  are not coated so as to allow for maximum heat transfer, and function to keep the solid pieces of ink separated during melting. This prevents coalescing of such pieces, which ordinarily would lump together and tend to clog the PTC heating device, as well as tend to increase the actual melting times. The folded fins  322 ,  324  also serve to increase the melting surface area, thus making the PTC heating device  310  more efficient. 
     The PTC heating device  310  is self-regulating because it can switch from a low resistance to a very high resistance as its temperature Ti and the temperature Tw of the solid pieces of phase change ink reach a prescribed limit. Switching off the current flow to the heating elements or folded fins  322 ,  324  effectively allows them to then cool. However, the temperature of the folded fins  322 ,  324 , will remain at the control temperature Tc as long as current is being supplied to them, but the steady state current will remain at a reduced level in a no load (that is, no solid ink) condition. 
     However, when more and new solid pieces of phase change ink at a cooler temperature Tw are added onto the folded fins  322 ,  324  causing their temperature Ti to again drop below the control temperature Tc, current flow to the folded fins  322 ,  324  again resumes. In this application it is advantageous to keep solid pieces of phase change ink being melted at a material temperature Tw of about 160° C. The pill portion designed/compounded temperature of about 170° C. is therefore slightly higher than the expected material temperature of 160° C. The temperature of the folded fins  322 ,  324  however will drop to the heat of fusion temperature of the ink, which is about 110° C. during the melt process. The PTC heating device  310  consumes maximum power only when melting is occurring, after which power consumption drops to about 15% of the maximum power. 
     Each melter housing  302  is electrically insulative and thus serves to isolate the PTC heating device  310  from electrically shorting out on the aluminum frame  316  of the heating device  310 . The PTC heating device  310  of the present invention for example uses 70 volts for raising the temperature Ti of the folded fins  322 ,  324  to 170° C. This is sufficient for heating and melting solid pieces of phase change ink that make direct or indirect contact with the folded fins  322 ,  324 . 
     The PTC temperature Ti rise time to the 170° C. is desirably less than 5 seconds and therefore results in immediate melting of the solid pieces of phase change ink making contact therewith. The material temperature Tw of the solid pieces of phase change ink first rises to the ink&#39;s heat of fusion at 110° C. where it remains while the solid pieces melt to form a molten liquid ink. 
     The molten liquid ink then drops gravitationally from the folded fins  322 ,  324  and through the passages or channels  330  to the molten liquid ink storage and control assembly  400  located below the melter assembly  300  (FIG.  2 ). Since the molten ink drop is gravitational, the residence time against the folded—fins  322 ,  324  is relatively low or short. 
     The melter assembly  300  also includes a heat retaining frame  220  for melting away solid ink pieces from the wall  302  in order to prevent ink build up on the inside walls of the melter housing. Such a build up ordinarily will interfere with solid ink pieces reaching the heating device  310 . The pieces are melted by making contact with the heat retaining frame  220  which is made for example of aluminum, and is located peripherally within the melter housing  302 . The heat retaining frame  220  is heated by the heat conduction through the fins making contact, and by convection losses of the melter assembly  300  and operates to keep melting solid pieces of ink away from the inside walls of the melter housing  302 . Periodically when solid ink pieces have been fed to through the pre-melter assembly  200  to the melter assembly  300 , the heating device (not shown) of the melter assembly will be turned on and kept on until the solid ink pieces are sufficiently melted. This ensures that the feed pipes  206 A,  206 B,  206 C,  206 D leading to the melter assembly  300  do not clog, and that melted ink does not coalesce on the inside walls of melter housing  302 . 
     As can be seen, there has been provided a solid phase change ink melter assembly is provided in a phase change ink image producing machine. The solid phase change ink melter assembly includes (a) a melter housing having walls defining a melting chamber; and (b) a positive temperature coefficient (PTC) heating device mounted within the melting chamber for heating and melting solid pieces of phase change ink into melted molten liquid ink 
     While the embodiment of the present invention disclosed herein is preferred, it will be appreciated from this teaching that various alternative, modifications, variations or improvements therein may be made by those skilled in the art, which are intended to be encompassed by the following claims: