Heat exchange unit for a printing system

Abstract

A heat exchange unit and a printing system containing the heat exchange unit, including a heat exchange region, a first print media transport path configured for transporting in operation a first print medium from a supply through the heat exchange, the heat exchange unit further containing a stationary heat exchange member, having a first side facing said first print media transport path and a second opposite side facing said second print media transport path, wherein, in operation, the second print medium is at an elevated temperature with respect to the first print medium and wherein, the first and second print medium have a heat exchange contact in the heat exchange region.

Claims

1. A heat exchange unit, comprising: a heat exchange region; a first print media transport path configured for operatively transporting a first print medium from a supply through the heat exchange region to a print engine; a second print media transport path configured for operatively transporting a second print medium from the print engine through the heat exchange region; a stationary heat exchange member in the form of a flexible foil having a first side facing said first print media transport path and a second, opposite side facing said second print media transport path, wherein, in operation, the second print medium conveyed from the print engine is at an elevated temperature with respect to the first print medium conveyed from the supply and wherein the first and second print medium are placed in heat exchange communication in the heat exchange region; and a pressing device configured to apply pressure to the second print medium in the second print media transport path in the direction of the first print media transport path such that the flexible foil deforms in order to follow the form of the first and second print media.

2. The heat exchange unit according to claim 1, wherein said first and second print media transport paths are configured such that, in an operative state in the heat exchanging region, said first print media is transported in a direction opposite to the direction of said second print media.

3. The heat exchange unit according to claim 1, wherein the first and second print media transport paths define a print media transport path, wherein a rotatable print media guiding member, positioned adjacent to the exit of any of said first and second print media transport paths, extends radially into the print media transport path.

4. The heat exchange unit according to claim 1, wherein a heater element is positioned adjacent to said first print media transport path in said heat exchange region.

5. The heat exchange unit according to claim 1, wherein the first media transport path extends contiguous to the second print media transport path.

6. A printing system in which a cold print medium is introduced from a supply in a first print media transport path, to a printing process and removed from said printing process as a print medium of elevated temperature, defining a second print media transport path, said first print media transport path extending contiguous to the second print media transport path, said printing system comprising: a heat exchange unit providing heat exchange communication between the cold print medium and the print medium having said elevated temperature, said heat exchange unit including a flexible foil having a first side facing said first print media transport path and a second, opposite, side facing said second print media transport path, whereby the thermal energy of the print medium having the elevated temperature is transferred to the cold print medium to preheat the cold print medium, and resulting in the cooling of the print medium of elevated temperature; a pressing device configured to apply pressure to the second print medium in the second print media transport path in the direction of the first print media transport path such that the flexible foil deforms in order to follow the form of both print media.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be explained with reference to the following drawings, wherein.

(2) FIG. 1 is a schematic view showing a printing system comprising a heat exchange unit according to an embodiment of the present invention;

(3) FIG. 2 is a schematic view of the heat exchange process according to an embodiment of the present invention;

(4) FIG. 3 is a schematic view of a heat exchange unit according to an embodiment of the present invention;

(5) FIGS. 4a and 4b are schematic views of a heat exchange unit comprising rotatable guiding members according to an embodiment of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a schematic view showing a printing system comprising a heat exchange unit according to an embodiment of the present invention. The printing system 1 has an engine 2 into which the paper is fed from a supply 3, preconditioned and printed with a printing process 50 and fed to a take-out area from which an operator can remove the printed media. The printing system 1 delivers marking material onto the print media in an image-wise fashion. This image can be fed, e.g., by a computer via a wired or wireless network connection (not shown) or by means of a scanner 7. The scanner 7 scans an image that is fed into the automatic document feeder 6 and delivers the digitized image to the printing controller (not shown). This controller translates the digital image information into control signals that enable the controller to control the marking units that deliver marking material onto an intermediate member. A preheated print medium is fed along the intermediate member, from which the image-wise marking material image is transferred onto the print medium. This marking material image is fused onto the print medium in a fuse step under elevated pressure and temperatures. The image bearing print medium is cooled down to a lower temperature before the print medium is delivered to the take-out area 4. A user-interface 5 enables the operator to program the print job properties and preferences such as the choice for the print medium, print medium orientation and finishing options. The printing system 1 has a plurality of finishing options such as stacking, saddle stitching and stapling. The finishing unit 8 executes these finishing operations when selected. It will be clear to a person skilled in the art that other image forming processes wherein an image of marking material is transferred onto a print media, possibly via one or more intermediate members, e.g., electro(photo)graphic, magnetographic, inkjet, and direct imaging processes are also applicable. The print media 11 that are delivered from the print process 50 are at an elevated temperature because of heating in the print process 50 and heating in the fusing step. The heat exchange unit according to the present invention uses the thermal energy of these outgoing print media for the preheating of cold media that have to be preheated before entering the print process 50. The outgoing printed media 11 are transported through a heat exchange zone in the heat exchange unit 20. FIG. 2 shows a schematic view of this principle. A print medium 10 that is separated from a supply unit 3 is transported to the print process 50 in the direction marked with arrow X. The thermal energy of the printed media 11 that originates from the print process and the fuse step is donated to the cold print media 10 through a thermal intermediate 13. While cooling the printed medium 11 down to an acceptable temperature in which the marking material is hardened and therefore less sensitive to smearing, the printed medium 11 is transported in the direction marked with arrow Y towards the take-out area 4 of the printing system 1.

(7) FIG. 3 is a schematic view of a heat exchange unit according to an embodiment of the present invention. A print medium is separated from a supply unit 3 and fed into the first print media transport path 23 of the heat exchange unit 20 in the direction of arrow I. This entry into the heat exchange unit is registered by sensor 25. The print medium is moved into pinch 21, which pushes the print medium through the first print media transport path 23 towards pinch 22. Pinch 22 draws the print medium from area 23 towards the print process (not shown) in the direction of arrow II. Inside the print process the print medium is pre-heated by an electric pre-heater (not shown) to facilitate the image-wise application of marking material which is fused into the print medium under elevated pressure and temperature. Both the application of the marking material and the fusing of the marking material onto the print medium increase the temperature of the print medium. The print medium at elevated temperature is then removed from the print process and fed into the second print media transport path 33 of the heat exchange unit in the direction of arrow III. Pinch 31 pushes the print media from the print process towards pinch 32. While the print media at elevated temperature is transported through the second print media transport path 33 a second print media is fed into the first print media transport path 23. As the first and second print media transport paths 23, 33 are having a heat exchange contact, the first print media at elevated temperature in the second print media transport path partially donates its thermal energy to the second print media in the first print media transport path 23 which receives the thermal energy and heats up. Because the first print medium donates thermal energy to the second print medium, the pre-heater of the print process can lower its thermal dissipation.

(8) In case of the absence of a print medium at an elevated temperature, e.g., at system start-up or after an interruption of print-activity, the heater element 27 can correct for the absence of the extra thermal energy as long as no print media at elevated temperature is available.

(9) To improve the exchange of thermal energy between print media at elevated temperature in the second print media transport path 33 and the cold media in the first print media transport path 23 a pressing member 35 applies pressure on the print media at elevated temperature such that the heat exchange efficiency increases. This pressure is sufficiently high to increase the heat exchange efficiency and sufficiently low as not to disturb the passage of the print media too much. Pressing member 35 is a foam layer that applies approximately 100-200 Pa of pressure on the print media. The heat exchange member begin stationary, i.e., the member does not move relative to the print media in the print media transport path, increases the efficiency of the heat exchange.

(10) To decrease the risk of smearing and cross-pollution of marking material from one print medium onto the other, a thin and flexible foil 28 is applied in between said first and second print media transport paths 23, 33. This thin flexible foil 28 is very smooth such that the print media are not obstructed while they are transported through the print media transport paths 23, 33. To prevent static charging of the print media the foil 28 has electro-conductive properties. The foil 28 is resistant to wear and has a low sliding resistance. To improve the thermal behavior of the foil 28 during the heat exchange between a first and a second print medium the foil is constructed very thin, such that the heating of the foil 28 itself does not obstruct the heat exchange between the print media. Therefore the heat capacity and thermal resistivity of the foil are adapted to exchange the heat between the first and second print media.

(11) FIGS. 4a and 4b show schematic views of a heat exchange unit comprising rotatable guiding members according to an embodiment of the present invention. The boxed area of FIG. 4a is enlarged and depicted in FIG. 4b. At the exits of the print media transport paths 23, 33 guiding members 41, 42 are rotatably connected with the heat exchange unit. Print media 11 that are transported through the paper paths 23, 33 are initially pushed respectively by pinches 21 and 31 until the print media are fed into drawing pinches 22 and 32. These drawing pinches 22 and 32 draw the print media out of the print media transport paths 23 and 33. Because the print media inside of the print media transport paths 23, 33 are influenced by a certain amount of friction, this drawing out of the print media 11 will put stress on the print media when drawn out. Especially at the curved exit areas of the print media transport paths 23, 33, this stress can occur. The freely rotatable guide members 41 and 42 decrease the stress on the print media 11 at these areas, thereby decreasing the risk of affecting the print media and image integrity.

(12) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.