Patent Publication Number: US-8112025-B2

Title: Cooling device and cooling method for a printing substrate in an electrographic printer or copier

Description:
BACKGROUND 
     The preferred embodiment concerns a cooling device and a cooling method for a printing substrate in an electrographic printer or copier. 
     Workflow printer or copiers are known (see for example WO 98/39691 A1). In such a printer or copier, charge images of the images to be printed are generated on a charge image carrier (for example a photoconductor belt). The charge image carrier is subsequently moved past developer stations, respectively once per color. For example, these transport developer comprised of toner and carrier to the charge image carrier. The toner migrates onto the charge image carrier corresponding to the charge images and inks these. The toner images are transfer-printed onto a printing substrate in the next step and are fixed on this. The precise workflow of the printing method can be learned from WO 98/39691 A1, the content of which is herewith incorporated into the disclosure. 
     A thermofixing is normally used to fix toner images onto the printing substrate. For example, fixing rollers (of which at least one is heated) are used for this, or infrared radiators are used as a heat source. The thermofixing of the toner images on the printing substrate requires that the printing substrate still exhibit a temperature of, for example, 120° C. or higher upon leaving the fixing station, such that a further processing of the printing substrate is difficult. In order to remedy this disadvantage, it is known to cool the printing substrate after the fixing station. 
     According to DE 42 35 667 C1, cooled air is blown onto the printing substrate to cool the printing substrate. The cooling device used for this possesses cooling surfaces provided with openings. Cold air is supplied to the openings via an air guide channel, flows out from the openings below the printing substrate and there forms a cooling air cushion. Air is simultaneously blown onto the other side of the printing substrate, and in fact counter to the travel direction of the printing substrate. 
     Additional cooling devices are known from, for example: DE 38 38 021 C2; EP 0 758 766 B1; DE 201 19 854 U1; U.S. Pat. Nos. 6,907,220 B2; 6,567,629 B2. For example, there aerators are used to cool a printing substrate, or externally or internally cooled rollers. 
     SUMMARY 
     It is an object to specify a cooling device for a printing substrate that is arranged at the output of a fixing station, is thereby executed in a compact manner and in spite of this sufficiently cools the printing substrate at high speed of the printing substrate. 
     In a cooling device for a printing substrate after passage through a fixing station, a transport path is provided for the printing substrate. A first cooling unit is provided along one side of the transport path. The first cooling unit has a first perforated plate facing towards the printing substrate, a coolant being conducted through the perforated plate. A second cooling unit is provided along an opposite side of the transport path. This second cooling unit has a perforated plate on a surface facing towards the printing substrate. A coolant is conducted through the perforated plate onto the opposite side of the printing substrate. A nip unit for the printing substrate has a nip roll integrated into the second cooling unit such that the nip roll is cooled by the second cooling unit. 
     An exemplary embodiment is presented in drawing figures hereafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the cooling device; 
         FIG. 2  is a side view of the cooling device; 
         FIG. 3  is a cooling device in which one part is folded down; 
         FIG. 4  is a coupling; and 
         FIG. 5  is a front view of a perforated plate used in the cooling device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment/best mode illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated as would normally occur to one skilled in the art to which the invention related are included. 
     The cooling device for a printing substrate is arranged at the output of the fixing station. It additionally cools a nip roll. 
     The cooling device has a transport path for the printing substrate. A first cooling unit connected with a first coolant medium source is provided along one side of the transport path for the printing substrate. This cooling unit has a first perforated plate on the surface facing towards the printing substrate, through which perforated plate a coolant can be conducted onto the one side of the printing substrate. A second cooling unit connected with a second coolant source is provided along the other, opposite side of the transport path for the printing substrate, which unit has a second perforated plate on the surface facing towards the printing substrate, through which perforated plate a coolant can be conducted onto the other side of the printing substrate. A nip unit for the printing substrate that has a nip roll is integrated into the second cooling unit, such that the nip unit is cooled by the first and/or second cooling unit. 
     Such a realization of the cooling device enables a compact design with a short cooling path that on the one hand is sufficient to cool the printing substrate even at high print speed so that the printing substrate can be processed further, and on the other hand the nip roll is also cooled. If the printing substrate is placed on the nip roll, it is additionally, advantageously cooled by this. 
     For a compact design it is advantageous if the first and second coolant sources are combined into a common coolant source. Furthermore, it is advantageous when the second cooling unit is arranged adjacent and next to the coolant source and the first cooling unit is arranged above the coolant source, since then the feed of the coolant can be implemented via short cooling tubes, for example. 
     Cooled air can appropriately be provided as a coolant, and a cooled air source in which, for example, a ventilator is arranged to move the cooled air, can be used as a coolant source. 
     In order to be able to access the individual structural units of the cooling device, and in order to be able to exchange the printing substrate in a simple manner, it is advantageous that the second cooling unit is executed such that it, together with the nip roll, can pivot away from the first cooling unit. 
     In particular, nozzle plates can be provided as perforated plates. 
     Cooling channels arranged parallel to the printing substrate can be used as a cooling unit, past which cooling channels the printing substrate is directed and which are connected via cooling tubes with the cooled air source. In order to comprehensively cool the printing substrate,
         the first cooling channel can have a nozzle plate on the one side facing the printing substrate, the nozzles of which nozzle plate are shaped such that the cooled air is accelerated towards the printing substrate;   the second cooling channel can have a perforated plate on the side facing the printing substrate, via the cooling holes of which perforated plate the cooled image archive is directed onto the printing substrate.       

     The cooling effect is additionally increased when the nip roll is also cooled. This can then absorb heat from the printing substrate and, for example, conduct it to the second cooling channel. This can be realized such that the nip roll is integrated into the second cooling channel. For this, the perforated plate can have a recess into which the nip roll is inserted such that only the surface facing towards the nip roll used to drive the printing substrate projects out from the second cooling channel. This embodiment has the advantage that the nip roll is part of the cooling device and is thereby used not only to transport the printing substrate but also for its cooling. Via this technique, the perforated plate is additionally sub-divided into two perforated plate sections, with the advantage that the printing substrate is cooled both before and after passing by the nip roll. The perforated plate sections thereby blow cooled air under the printing substrate (via the cooling holes) and generate an air cushion on which the printing substrate glides. 
     A roller saddle can be provided to guide the printing substrate past the nozzle plate of the first cooling channel. It is then appropriate to design the nozzle plate of the first cooling channel so that nozzle plate and roller plate run parallel to one another and form a transport path in which the printing substrate is taught, rests on the roller saddle and is directed through the roller saddle. In this way, a distance from nozzle plate to printing substrate can be set that is optimal for the cooling of the printing substrate. 
     In order to avoid unwanted heat bands on the printing substrate, the nozzles of the nozzle plate of the first cooling channel can be arranged offset relative to one another. This also applies for the cooling holes of the perforated plate, wherein the cooling holes of the two perforated plate sections can also lie offset relative to one another. 
     In order to simply design the pivoting of the second cooling channel with nip roll, the second cooling tube can be connected to the cooled air source via a coupling such that the connection of the second cooling tube with the cooled air source detaches upon pivoting away and the connection is reestablished upon pivoting towards. 
     In summary, the cooling device according to the preferred embodiment has the following advantages:
         The nozzle plate of the first cooling channel has air nozzles that accelerate the cooled air towards the printing substrate.   The cooling path is optimized so that the nip roll is integrated into the second cooling channel.   The nip roll is surrounded on all sides by the second cooling channel except for the contact surface facing towards the printing substrate. The nip roll can thus discharge the heat absorbed from the printing substrate to the second cooling channel; it serves as a cooling rib.   The two cooling channels can be supplied via one cooled air source.   The second cooling channel, together with the nip roll, can be folded down relative to the first cooling channel and the cooled air source. The access to the structural units of the cooling device is therefore simplified. In order to thereby make the handling easier, the second cooling tube can be connected with the cooled air source via a coupling.   The nozzles and the cooling holes are arranged offset relative to one another to avoid heat bands on the printing substrate.       

       FIG. 1  shows a device KE for cooling a printing substrate  10 , for example a paper web or a paper sheet, that is arranged at the output of a fixing station FX. Such a cooling device KE is, for example, provided at the output of a printing module; with regard to the design of a corresponding electrographic printing apparatus, refer to WO 98/39691 A1, which is herewith incorporated by reference into the disclosure of the present application. The cooling device KE has the object of cooling the printing substrate  10  at the output of the fixing station FX corresponding to the DE 42 35 667 C1; DE 42 35 667 C1 is herewith likewise incorporated by reference into the disclosure. 
     The fixing station FX according to  FIG. 1  has a fixing roller  11  and a contact pressure roller  12 . Toner images applied on the printing substrate  10  are fixed in a known manner according to the thermofixing method, meaning that the printing substrate  10  runs between the heated fixing roller  11  and contact pressure roller  12 , the contact pressure roller  12  presses the printing substrate  10  against the fixing roller  11  for fixing, and the toner images are fixed in the printing substrate  10  via heat and pressure. 
     When the printing substrate  10  leaves the fixing station FX, this printing substrate  10  still has a temperature of approximately 120° C. or more. A printing substrate  10  with such a temperature is not suitable for the post-processing devices. It is therefore known to cool the printing substrate  10  after the fixing station FX, for example via a device according to DE 42 35 667 C1. A cooling device KE that sufficiently cools the printing substrate  10  even at high speeds is now specified by the preferred embodiment. 
     The cooling device KE is arranged at the output of the fixing station FX according to  FIG. 1 . It has the following units:
         on the one side or surface of the printing substrate  10  (for example the printed front side of a printing substrate web), a first cooling unit KM 1  for cooling this side;   on the other side of the printing substrate  10  (for example the back side of a printing substrate web), a second cooling unit KM 2  for cooling this other side;   a source  13  for a coolant (for example cooled air) that is connected with both cooling unit KM 1 , KM 2 ;   additionally, a roller saddle  14  that is arranged at the output of the fixing station FX and that directs the printing substrate  10  past the first cooling means KM 1 ;   a nip unit AE for the printing substrate  10  at the output of the cooling device KE, which nip unit AE draws the printing substrate  10  past the cooling units KM 1 , KM 2 .       

     The first cooling unit KM 1  has a first cooling channel  15  that provides a nozzle plate  16  facing towards the printing substrate  10 , via which nozzle plate  16  the coolant (cooled air in the following) is blown towards the printing substrate  10 . The first cooling channel  15  is connected with the coolant source (in the following a cooled air source  13 ) via a first cooling hose  17 , for example. The nozzle plate  16  has nozzles  18  arranged offset relative to one another. These nozzles  18  are shaped so that the cooled air is accelerated towards the printing substrate  10  in the first cooling channel  15 . The nozzle plate  16  is shaped corresponding to the roller saddle  14 ; for example, if the roller saddle  14  is executed curved a corresponding to  FIG. 1 , the nozzle plate  16  is executed with corresponding curve so that a transport gap  19  ( FIG. 2 ) of the same distance as the transport path for the printing substrate  10  arises between nozzle plate  16  and roller saddle  14 . The first cooling channel  15  is, for example, essentially executed square; however, it can also exhibit a different cross-section. The transport path can, at least in sections, have a distinctly larger width than the thickness of the printing substrate  10 . 
     The printing substrate  10  is transported through the transport gap  19  in the direction  10   a . The cooling units KM 1  and KM 2  are arranged on opposite sides along the transport gap  19 . 
     The second cooling unit KM 2  is realized as a second cooling channel  20  that is connected with the cooled air source  13  via a second cooling tube  21 , for example. The second cooling channel  15  has a perforated plate  22  with cooling holes  23  facing towards the printing substrate  10 , via which cooling holes the cooled air is blown towards the other side (for example back side) of the printing substrate  10 . The perforated plate  22  is shaped such that an air cushion on which the printing substrate  10  can glide can form between printing substrate  10  and perforated plate  22 . 
     The nip unit AE has a nip roll  24  and a contact pressure roller  25 . The contact pressure roller  25  draws the printing substrate  10  through the cooling device KE. In order to be able to cool the nip roll  24 , this is integrated into the second cooling channel  20  such that the second cooling channel  20  surrounds the nip roll  24  except for the contact surface  26  used to transport the printing substrate  10 . The perforated plate  22  is thereby sub-divided into two perforated plate regions  22   a ,  22   b  between which the nip roll  24  is arranged, such that the nip roll  24  projects beyond the perforated plate  22  and therefore can engage the printing substrate  10 . The contact pressure roller  24  can be constructed from individual wheels  27 , for example. 
     The cooled air source  13  is arranged adjacent and next to the second cooling channel  20 , such that the connection between cooled air source  13  and second cooling channel  20  via the second cooling tube  21  is short. In contrast to this, the first cooling channel  15  is arranged above the cooled air source  13 . The two cooling unit KM 1 , KM 2  and the nip unit AE are thus arranged relative to one another so that the entire cooling device KE achieves an optimal cooling with a minimal space requirement and short cooling path. 
     To cool the printing substrate  10 , this is initially directed past the first cooling channel  15  via the roller saddle  14  such that the one side of the printing substrate  10  is cooled. The printing substrate  10  is subsequently drawn by the nip unit AE past the second cooling channel  20 , and the other side (for example back side) of the printing substrate  10  is thereby cooled. 
       FIG. 2  shows the cooling device KE from the side. The contact pressure roller  12  is thereby shown folded down from the fixing roller  11 . The first cooling channel  15  is arranged opposite the roller saddle  14 ; and cooled air is blown onto the printing substrate  10  via the nozzles  18  of the nozzle plate  16 . The nozzles  18  are shaped according to  FIG. 2  such that the cooled air is accelerated towards the printing substrate  10 ; for example, the nozzles  18  taper towards the printing substrate  10 . The cooled air is symbolically represented by lines  28  in  FIG. 2 . The roller saddle  14  is arranged opposite the nozzle plate  16 , which roller saddle  14  is, for example, formed by guide roller  29  situated next to one another as seen in the movement direction of the printing substrate  10 . 
     The second cooling channel  20  is supplied with cooled air (lines  30  in  FIG. 2 ) via the cooling tube  21 . To accommodate the nip roll  24 , the second cooling channel  20  has a recess  31 . The second cooling channel  20  thus completely surrounds the nip roll  24  except for the contact surface  26 , with the result that the nip roll  24  is cooled by the cooled air  30 . The nip roll  24  extracts heat energy from the printing substrate  10  via heat conduction, which heat energy it passes to the second cooling channel  20 . Since the nip roll  24  continuously rotates in the second cooling channel  20 , it is continuously washed by cooled air and can thereby dissipate the heat absorbed from the printing substrate  10  very well. The printing substrate  10  is thus optimally cooled on its other side by the perforated plate sections  22   a ,  22   b  and the nip roll  24 . 
     Furthermore, the cooled air source  13  is recognizable from  FIG. 2 ; it has a pivot axle  32  on which the second cooling channel  20  and the nip roll  14  can be pivoted downward. Furthermore, from  FIG. 2  it can be learned that the second cooling channel  20  is arranged next to the cooled air source  13  and is connected with the cooled air source  13  on a short path via the second cooling tube  21 . 
       FIG. 3  shows the cooling device KE given a second cooling channel  20  pivoted away. In order to arrive in this position, the second cooling channel  20  is pivoted away from the contact pressure roller  25 . In this pivoting process, the connection of the second cooling tube  21  with the cooled air source  13  is released. For this a coupling  33  is provided that has two coupling pieces  34 ,  35  in the shape of half shells, wherein one coupling piece  34  is associated with the cooled air source  13  and the other coupling piece is associated with the second cooling tube  21 . Via rotation, the coupling pieces  34 ,  35  can be detached from one another or can be connected with one another. A realization of the coupling  33  can be learned from  FIG. 4 ; there both coupling pieces  34 ,  35  are shown, wherein the one coupling piece  34  is connected with the cooled air source  13  and the coupling piece  35  is connected with the second cooling tube  21 . Each coupling piece  34 ,  35  has a half shell, wherein the two half shells are matched to one another so that the two half shells detach from one another or engage in one another via rotation. 
     Furthermore, the connection of the first cooling channel  15  with the cooled air source  13  via the first cooling tube  17  can be learned from  FIG. 3 . The first cooling channel  15  is arranged above the cooled air source  13  and is connected with the cooled air source  13  via the first cooling tube  17 . From  FIG. 3  it arises that long, glossy cooling tubes  17 ,  21  are avoided via the optimal arrangement of the cooling channels  15 ,  20  relative to the cooled air source  13 . 
     For the preferred embodiment of the invention the perforated plate  22  can be learned from  FIG. 5 . In the upper perforated plate section  22   a , the cooling holes  23  lie offset from one another within groups; in the lower perforated plate section  22   b , the cooling holes  23  lie atop one another in groups. The groups of cooling holes in the upper and lower perforated plate sections  22   a ,  22   b  are additionally arranged offset relative to one another. Via selection of the position of the cooling holes  23 , it can be achieved that the printing substrate  10  is cooled as desired; for example, the creation of heat bands on the printing substrate  10  can be prevented. 
     While preferred embodiments have been illustrated and described in detail in the drawings and foregoing description, the same are to be considered as illustrative and not restrictive in character, it being understood that only two preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected.