Abstract:
An image transfer printing apparatus, including: a member having an imaging transfer surface; an applicator assembly distributing a liquid layer onto the imaging transfer surface to produce an intermediate transfer surface; the applicator assembly including a porous member having a core, the core having openings defined therein, a liquid supply system connected to the core for supplying liquid to saturate the porous member.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates generally to a drum for fixing an ink image on a receiving medium and, more particularly, to applicator assembly having a foam oil donor roll and method to control oil level thereof.  
       BACKGROUND OF THE INVENTION  
       [0002]     For printing in a solid-ink printer, a common method of applying droplets of ink onto a piece of paper is to directly print the image onto the paper, i.e., a process known as direct printing. Ink jet printing systems utilizing intermediate transfer ink jet recording methods, such as that disclosed in U.S. Pat. No. 5,389,958 entitled IMAGING PROCESS and assigned to the assignee of the present application is an example of an indirect or offset printing architecture that utilizes phase change ink. A release agent application defining an intermediate transfer surface is applied by a wicking pad that is housed within an applicator apparatus. Prior to imaging, the applicator is raised into contact with the rotating drum to apply or replenish the liquid intermediate transfer surface.  
         [0003]     Once the liquid intermediate transfer surface has been applied, the applicator is retracted and the printhead ejects drops of ink to form the ink image on the liquid intermediate transfer surface. The ink is applied in molten form, having been melted from its solid state form. The ink image solidifies on the liquid intermediate transfer surface by cooling to a malleable solid intermediate state as the drum continues to rotate. When the imaging has been completed, a transfer roller is moved into contact with the drum to form a pressurized transfer nip between the roller and the curved surface of the intermediate transfer surface/drum. A final receiving substrate, such as a sheet of media, is then fed into the transfer nip and the ink image is transferred to the final receiving substrate.  
         [0004]     In this standard offset process, the release agent application must be applied to every print. This provides a release layer that facilitates image transfer. Therefore, unlike a typical laser printer process in which the deposition of the toner onto the paper and the fusing of the paper occurs in parallel (at the same time), the current solid-ink process operates in series.  
         [0005]     Existing applicator assembly and oiling methods employ an impregnated foam or capillary media roll that is brought into contact with the image drum forming a nip and thereby displacing oil from the pores to the drum. It is then wiped to a consistent level using a urethane blade. The existing method results in oil levels that are too high for some applications. The high oil levels result in a variety of issues such as offset, reduced gloss, expense, reduced foam roll life etc. In response to this issue, applicants have explored using traditional RAM&#39;s to meter oil onto the image drum. Applicants have found that this method is prone to contamination (due to the solubility of the ink with silicone oil) and is an expensive design in comparison to a foam roll system.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention obviates the problems noted above by utilizing a system in which a porous oil donor roll  15  loaded to a low saturation level and the fluid level is controlled by monitoring the mass of the roll and refilling when the mass drops below a predetermined level. In the embodiment shown, this is accomplished by weighing the roll with a spring loaded rocker arm and sensor. The roll design employs a porous drip tube through the middle, and because the oil in the roll can be refilled, Applicants have found that the roll has much longer life than the method used in the current products, which rely on loading a roll with oil and counting the number of prints before replacing the roll.  
         [0007]     Still other aspects of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described a preferred embodiment of this invention by way of illustration of one of the modes best suited to carry out the invention. The invention is capable of other different embodiments and its details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The objects, features and advantages of the invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when it is taken in conjunction with the accompanying drawings.  
         [0009]      FIG. 1  is a diagrammatic illustration for applying a two-step transfix process in an ink jet printing system.  
         [0010]      FIG. 2  is a schematic illustrating the applicator of the present invention.  
         [0011]      FIG. 3  is a schematic illustrating the oiling sensor employed with the present invention.  
         [0012]      FIG. 4  illustrates experimental data using the applicator of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  discloses a diagrammatical illustration of an imaging apparatus  10  of the present invention for applying a two-step transfix process whereby a hot melt ink is printed onto an elastomer or metal transfer surface for transference to a receiving substrate and then transported through a fuser for post fusing. Referring to  FIG. 1  wherein like numerals refer to like or corresponding parts throughout, there is shown a printhead  11  having ink jets supported by appropriate housing and support elements (not shown) for either stationary or moving utilization to deposit ink onto an intermediate transfer surface  12 . The ink utilized is preferably initially in solid form and then changed to a molten state by the application of heat energy to raise the temperature from about 85 degrees to about 150 degrees centigrade. Elevated temperatures above this range will cause degradation or chemical breakdown of the ink. The molten ink is then applied in raster fashion from ink jets in the printhead  11  to the intermediate transfer surface  12  forming an ink image. The ink image is then cooled to an intermediate temperature and solidifies to a malleable state wherein it is transferred to a receiving substrate or media  28  and then post fused. The details of this process will now be more fully described below.  
         [0014]     In accordance with the present invention, a drum  14  which is shown in  FIG. 1  has affixed an outer compliant elastomer layer  9  defining a release surface. The intermediate transfer surface  12  is a liquid layer applied to the outer compliant elastomer layer  9  on drum  14  by contact with an applicator assembly  16 . By way of example, but not of limitation, applicator assembly  16  comprises a wicking roller impregnated with a release liquid for applying the liquid and a metering blade  18  for consistently metering the liquid on the surface of the drum  14 . Suitable release liquids that may be employed to form the intermediate transfer surface  12  include water, fluorinated oils, glycol, surfactants, mineral oil, silicone oil, functional oils or combinations thereof. As the drum  14  rotates about a journalled shaft in the direction shown in  FIG. 1 , applicator assembly  16  is raised by the action of an applicator assembly cam and cam follower (not shown) until the wicking roller is in contact with the surface of the drum  14 .  
         [0015]     Referring once again to  FIG. 1 , the release liquid that forms the intermediate transfer surface  12  on outer compliant elastomeric layer  9  is heated by an appropriate heater device  19 . The heater device  19  may be a radiant resistance heater positioned as shown or positioned internally within the drum  14 . Heater device  19  increases the temperature of the intermediate transfer surface  12  from ambient temperature to between 25 degrees to about 70 degrees centigrade or higher to receive the ink from printhead  11 . This temperature is dependent upon the exact nature of the liquid employed in the intermediate transfer surface  12  and the ink used and is adjusted by temperature controller  40  utilizing thermistor  42 . Ink is then applied in molten form from about 85 degrees to about 150 degrees centigrade to the exposed surface of the liquid intermediate transfer surface  12  by the printhead  11  forming an ink image  26 . The ink image  26  solidifies on the intermediate transfer surface  12  by cooling down to the malleable intermediate state temperature provided by heating device  19 . A receiving substrate guide apparatus  20  then passes the receiving substrate  28 , such as paper or transparency, from a positive feed device (not shown) and guides it through a nip  29 . Opposing arcuate surfaces of a roller  23  and the drum  14  forms the nip  29 . In one embodiment, the roller  23  has a metallic core, preferably steel with an elastomer coating  22 . The drum  14  having the outer compliant elastomer layer  9  continues to rotate, entering the nip  29  formed by the roller  22  with the curved surface of the intermediate transfer surface  12  containing the ink image  26 . The ink image  26  is then deformed to its image conformation and adhered to the receiving substrate  28  by being pressed there against.  
         [0016]     The ink image  26  is first applied to the intermediate transfer surface  12  on the outer compliant surface  8  or rigid layer  9  and then transfixed off onto the receiving substrate or media  28 . The ink image  26  is thus transferred and fixed to the receiving substrate  28  by the pressure exerted on it in the nip  29  by the resilient or elastomeric surface  22  of the roller  23 . By way of example only, the pressure exerted may be less than 800 lbf on the receiving substrate or media. Stripper fingers  25  (only one of which is shown) may be pivotally mounted to the imaging apparatus  10  to assist in removing any paper or other final receiving substrate  28  from the exposed surface of the liquid layer forming the intermediate transfer surface  12 . After the ink image  26  is transferred to the receiving substrate  28  and before the next imaging, the applicator assembly  16  and metering blade  18  are actuated to raise upward into contact with the drum  14  to replenish the liquid intermediate transfer surface  12 .  
         [0017]     A heater  21  may be used to preheat the receiving surface  28  prior to the fixation of the ink image  26 . The heater  21  may be set to heat from between about 60 degrees to about 200 degrees centigrade. It is theorized that the heater  21  raises the temperature of the receiving medium to between about 90 degrees to about 100 degrees centigrade. However, the thermal energy of the receiving substrate  28  is kept sufficiently low so as not to melt the ink image upon transfer to the receiving substrate  28 . When the ink image  26  enters the nip  29  it is deformed to its image conformation and adheres to the receiving substrate  28  either by the pressure exerted against ink image  26  on the receiving substrate  28  or by the combination of the pressure and heat supplied by heater  21  and/or heater  19 . Additionally, a heater  24  may be employed which heats the transfer and fixing roller  23  to a temperature of between about 25 degrees to about 200 degrees centigrade. Heater devices  21  and  24  can also be employed in the paper or receiving substrate guide apparatus  20  or in the transfer and fixing roller  23 , respectively. The pressure exerted on the ink image  26  must be sufficient to have the ink image  26  adhere to the receiving substrate  28  which is between about 10 to about 2000 pounds per square inch, and more preferably between about 750 to about 850 pounds per square inch.  
         [0018]     After exiting the nip  29  created by the contact of the roller  23  and the outer compliant layer  9  and drum  14 , the ink image can then be thermally controlled with a thermal device  60 . This thermal device  60  can heat, cool, or maintain the temperature of the receiving substrate  28  and ink image  26  which may by way of example be between 50 to 100 degrees C. The highest temperature the receiving substrate  28  and ink image  26  can be increased to in this location is dependent on the melting or flash point of the ink and/or the flash point of the receiving substrate  28 . The thermal device  60  could be as simple as insulation to maintain the temperature of the ink and substrate as it exits the nip  29 , or a heating and/or cooling system to add or remove thermal energy. The receiving substrate  28  and ink image  26  are then transported to a fuser  52 . The fuser  52  is composed of a back-up roller  46  and a fuser roller  50 . The back-up roller  46  and fuser roller  50  have metallic cores, preferable steel or aluminum, and may be covered with elastomer layers  54  and  56 , respectively. The back-up roller  46  engages the receiving substrate  28  and ink image  26  on the reverse side to which the ink image  26  resides. This fuses the ink image  26  to the surface of the receiving substrate  28  so that the ink image  26  is spread, flattened, penetrated and adhered to the receiving substrate  28 . The pressure exerted by the fuser may be between 100 lbf to about 2000 lbf by way of example.  
         [0019]     When the receiving substrate  28  and ink image  26  enter the fuser  52  their temperature will change as determined by the transient heat transfer of the system during the dwell in a nip  51  formed by the fuser roller  50  and the back-up roller  46 . Depending on the temperature of the back-up roller  46  and fuser roller  50 , the transient temperature of the receiving substrate  28  and ink image  26  throughout their thickness can be controlled by either quenching or hot fusing. If the receiving substrate  28  and ink image  26  are brought into the fuser nip  51  hotter than the fuser roller  50  and the back-up roller  46 , the ink image  26  will be quenched to a cooler temperature. This is referred to as quench fusing. If the receiving substrate  28  and ink image  26  is brought into the fuser nip  51  cooler than the fuser roller  50  and the back-up roller  46 , the ink image  26  will be heated to a higher temperature, say between 75-100C. This is referred to as hot fusing. This process allows pressure to be applied to the receiving substrate  28  and ink image  26  at temperatures unachievable in the first nip  29 . This is done by quenching the receiving substrate  28  and ink image  26  from a high temperature, say 80-85C down to a lower temperature, say 55-65 C where the ink image  26  has enough cohesive strength to remain intact as it exits the fuser.  
         [0020]     Additionally, the above fusing process may also be accomplished by heating the secondary fuser nip  51  such that the ink image  26  near the surface of the receiving substrate  28  is hotter than the ink image near the surface of the fuser roller  50 . This allows cool enough ink temperatures for release from the fuser roller  50  and higher temperatures near the receiving substrate  28 , which increase spread, flattening, penetration and adhesion. In the case that the fuser roller  50  is a belt instead of a roller, the receiving substrate  28  and ink image  26  can be held against the belt for a distance past the nip  51  formed by the secondary fuser  50  and back-up roller  46 . This allows the ink sufficient time to cool to a temperature low enough to allow it to be stripped from the belt. It should be understood that the temperature of the fuser  52  can be different to that of the receiving substrate  28  and ink image  26  and is controlled with a separate control system  56  consisting of a heater  48 , and thermistor  54 , as is shown in  FIG. 1 . Stripper fingers  58  (only one of which is shown) may be pivotally mounted to the fuser roller  50  to assist in removing any paper or receiving substrate from the surface of the fuser roller  50 . The ink image  26  then cools to ambient temperature where it possesses sufficient strength and ductility to ensure its durability.  
         [0021]     Now focusing applicator of the present invention shown in  FIG. 2 , there is provided a foam oiling roll  100  having a core  102  with an internal porous drip tube  105  which is inserted in core  102 . The oil level in the foam roll  100  is controlled by controller  120  which is in communication with mass sensor  140  and pump  115 . Controller activates pump  115  to pumping oil to the tube  103  when the amount of oil in the roll falls below a desired value which is determined by mass sensor  140 .  
         [0022]     The present device attempts to provide a method of controlling oil levels using a metered supply from a foam roll. It has been found that if a foam roll is impregnated such that it has a low level of oil saturation (i.e. less than fully saturated), it gives up less oil to the image drum/metering blade combination, but still does it at a uniform level. The drawback to this is that if the oil level starts out low in the foam roll, then the life of the roll is severely diminished. This invention incorporates the use of an internal porous drip tube to supply oil to the roll at controlled rates where the signal to supply oil is provided by determining the amount of oil in the roll and turning the oil pump on when the amount goes below a predetermined level.  
         [0023]      FIG. 4  shows the comparison between foam rolls loaded with different oil at different amounts of impregnation vs. the oil on copy as measured by ICP analysis. As can be seen, there are two sets of curves. One set shows the effect of reducing foam loading on a smooth image drum, the other shows reduced level on a textured drum. It is likely that drums for split process solid ink (i.e. solid ink with an elastomer image drum) will have a textured surface in order to help control image quality issues such as drawback. As a result (mostly due to capillary action and the metering blade on image drum approach), the texture will inherently attempt to hold more oil. By adopting this method we can effectively negate some of the effects created by texturing the drum while still providing an inexpensive and reliably uniform solution to oiling of the solid ink image drum.  
         [0024]     There are many possible ways in which the amount of oil in the roll can be found. One such way is illustrated in  FIG. 3 . This uses mass sensor  140 , as the weight of the roll changes and becomes lighter, the spring  150  rotates the foam roll off of the cam  170  and thereby breaks the sensor beam produce by optical sensor  160 . This triggers the controller to initiate an algorithm to start the pump pumping.  
         [0025]     It should be clear that those skilled in the art would be able to conceive many viable options for detecting the change in the amount of oil and this is only one such method. Other methods may be to measure the torque to start or stop the foam roll and calculate the mass change from the change in inertia.  
         [0026]     While the invention has been described above with reference to specific embodiments thereof, it is apparent that many changes, modifications and variations in the materials, arrangements of parts and steps can be made without departing from the inventive concept disclosed herein. Accordingly, the spirit and broad scope of the appended claims is intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.