Abstract:
One embodiment is directed to a print media coating device that includes first and second web supplies, first and second web take-ups, and a fuser defining a media path therethrough. The first web supply and the first web take-up are positioned on one side of the media path and the second web supply and the second web take-up are positioned on the other side of the media path opposite the first web supply and the first web take-up. A first coating material web runs from the first web supply, along the media path through the fuser, to the first web take-up and a second coating material web runs from the second web supply, along the media path through the fuser, to the second web take-up. Another embodiment is directed to a method for coating print media that includes sandwiching the print media between two layers of coating material and then fusing the coating material to the print media.

Description:
FIELD OF THE INVENTION 
     The invention is directed to devices and methods for coating both sides of print media. 
     BACKGROUND 
     It is sometimes desirable to coat printed media with a film of clear flexible material. Such coatings can be formulated and applied to help protect the printed image, enhance the printed image, provide a more uniform gloss level across the entire media (including both printed and unprinted areas) or expand the color gamut in the printed areas. Duplex printing in which printed images are applied to both sides of a sheet of paper or other print media is now very common. Many printers, copiers, multi-function peripherals and other printing devices offer duplex printing. Where a coating is desired on both sides of a sheet, such as might be the case with duplex printing, the sheet must pass through the coating module of a post print finishing device twice—once to coat the top of the sheet and once to coat the bottom of the sheet. 
     SUMMARY 
     Various embodiments of the present invention were developed in an effort to improve on conventional techniques for coating print media on two sides. Accordingly, one embodiment of the present invention is directed to a print media coating device that includes first and second web supplies, first and second web take-ups, and a fuser defining a print media path therethrough. The first web supply and the first web take-up are positioned on one side of the media path and the second web supply and the second web take-up are positioned on the other side of the media path opposite the first web supply and the first web take-up. A first coating material web runs from the first web supply, along the media path through the fuser, to the first web take-up and a second coating material web runs from the second web supply, along the media path through the fuser, to the second web take-up. 
     Another embodiment of the invention is directed to a method for coating print media that includes sandwiching the print media between two layers of coating material and then fusing the coating material to the print media. 
     Coating print media on two sides with a single pass through a coating device helps reduce the coating time and maintain more consistent gloss levels on both sides of the media compared to dual pass devices. Some of the embodiments described also allow for the application of coatings to both sides of continuous roll-type print media that cannot pass through a coating device twice. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a device for simultaneously coating both sides of a sheet of print media according to one embodiment of the invention. 
     FIG. 2 illustrates a coating material web. 
     FIG. 3 illustrates a device for simultaneously coating both sides of a sheet of print media according to one embodiment of the invention in which the device includes cooling rollers and peel bars. 
     FIG. 4 illustrates a modular coating device according to one embodiment of the invention installed in a post print finishing device. 
     FIG. 5 is a more detailed illustration of a coating device such as the one shown in FIG.  4 . 
     FIG. 6 illustrates the fuser and cooler module of a coating device such as the one shown in FIG.  4 . 
     FIG. 7 illustrates a modular coating device according to one embodiment of the invention installed in a post print finishing device attached to a printer. 
     FIG. 8 is a perspective view of an upper/top side coating module according to one embodiment of the invention. 
     FIG. 9 illustrates a drive train for the driven components of a modular coating device according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a device for simultaneously coating both sides of a sheet of print media according to one embodiment of the invention. Referring to FIG. 1, coating device  10  includes first/top side coating material web supply and web take-up spools  12  and  14  and second/bottom side coating material supply and take-up spools  16  and  18 . A first/top side coating material web  20  runs from top supply spool  12  through a fuser  22  to top take-up spool  14 . A second/bottom side coating material web  24  runs from bottom web supply spool  16  through fuser  22  to bottom web take-up spool  18 . Webs  20  and  24  represent generally any web that carries a coating film suitable for use with paper and other types of print media. FIG. 2 is a section view illustrating a typical web suitable for use in coating device  10 . Referring to FIG. 2, web  20 / 24  includes a layer of adhesive material  26 , a layer of coating material  28  on adhesive layer  26 , a carrier  30  or backing as it is sometimes called and a release layer  32  interposed between carrier  30  and coating material  28 . Suitable webs include, for example, the clear flexible film webs described in pending Hewlett-Packard patent application Ser. No. 10/167,891 filed Jun. 11, 2002 and titled “Images Printed On Porous Media And Coated With A Thermal Transfer Overcoat.” 
     Fuser  22  represents generally any suitable device for applying heat or pressure or both to the web/media sandwich to cause coating  28  to bond to the paper or other print media. In the embodiment illustrated in FIG. 1, fuser  22  includes a pair of opposing rollers  34  and  36  that rotate against one another to form a fuser nip  40 . A conventional fuser such as the roll type fuser used in a laser printer may be adapted for use as fuser  22  in coating device  10 . In one example of such a fuser, which is shown in FIG.  1  and in more detail in FIG. 6, roller  34  is constructed as a heated fuser roller and roller  36  is constructed as a compliant pressure roller. 
     When a coating across the full width of the paper or other print media  42  is desired, as will typically be the case, each web  20  and  24  and the corresponding supply and take-up spools are about the same width as the print media, as best seen in FIG.  6 . Print media sheet  42  moves through fuser  22  along a media path  44 . Top web  20  moves from top web supply spool  12  through fuser  22  to top web take-up spool  14  along a first/top web path  46 . Bottom web  24  moves from bottom web supply spool  16  through fuser  22  to bottom web take-up spool  18  along a second/bottom web path  48 . Print media path  44  and web paths  46  and  48  converge at fuser nip  40 , are coincident with one another through fuser  22  as coating  28  from each web is applied to the top and bottom of print media sheet  42 , and then diverge as each now spent web  20   a  and  24   a  is taken up to take-up spools  14  and  18 . The combination of heat and pressure applied to webs  20  and  24  and media sheet  42  as they pass through fuser nip  40  melts adhesive layers  26  into sheet  42  to bond coating  28  to the top and bottom of the sheet  42  and softens release layers  32 . Spent webs  20   a  and  24   a  that are taken up on spools  14  and  18  consist of carriers  30  and the remnants of release layers  32 . 
     FIG. 3 illustrates a coating device  10  constructed according to a second embodiment of the invention. In this embodiment, webs  20  and  24  and sheet  42  pass through a cooler  50  downstream from fuser  22  and over peel bars  52  and  54  downstream from cooler  50 . Print media path  44  and web paths  46  and  48  converge at fuser nip  40 , are coincident with one another through fuser  22  and cooler  50 , and then diverge at peel bars  52  and  54  as each now spent web  20   a  and  24   a  is taken up to take-up spools  14  and  18 . Cooler  50  cools webs  20  and  24  and sheet  42  to accelerate curing the bond between the coating layers  28  and sheet  42 . Accelerated curing strengthens the bond between coating  28  and sheet  42  and allows carrier  30  to separate more cleanly from coating  28  at peel bars  52  and  54 . 
     In the embodiment of FIG. 3, cooler  50  is constructed as a pair of opposing rollers  56  and  58  that rotate against one another to form a cooler nip  60 . Cooler  50  may cool passively as a heat sink, in which case cooler rollers  56  and  58  are constructed as a relatively large mass of thermally conductive material. Alternatively, one or both cooler rollers  56  and  58  are actively cooled so that cooler  50  actively cools the web/sheet sandwich as it passes between the cooled cooler rollers  56  and  58 . 
     Downstream from cooler  50 , each web  20 ,  24  passes over a peel bar  52 ,  54 . Each peel bar  52  and  54  extends across the width of the web and protrudes slightly into the web path. Each web path  46  and  48  diverges from media path  44  at peel bars  52  and  54  at a sharp angle θ, preferably 60° to 130° and most preferably about 90°, to help carrier  30  break more cleanly away from coating layer  28 . 
     In the embodiment of FIG. 3, peel bars  52  and  54  are not aligned directly opposite one another across the web/media path. It has been discovered that the staggered configuration shown in FIG. 3, in which one peel bar is located downstream from the other peel bar, helps improve carrier/coating separation. In an alternative configuration in which the peel bars are placed directly opposite one another, each carrier  30  is peeled away from coating layer  28  at the same time. It was discovered during testing of this alternative configuration that the adhesion between carrier  30  and coating  28  is such that each web  20  and  24  tends to pull on media sheet  42  as carrier  30  peels away from coating  28 . This pull is not always the same on each side of sheet  42 . One side pulling harder than the other tends to relieve pressure on the weak side peel bar. This pressure relief can impede separation between carrier  30  and coating  28  on the weak side which can, in turn, affect the quality of the coating retained on that side of sheet  42 . Hence, the staggered configuration for peel bars  52  and  54  is preferred over the aligned configuration. 
     FIGS. 4-7 illustrate a modular coating device  62  installed in a post-print finishing device  64  operatively coupled to a printer  66 . FIG. 5 is an enlarged view of coating device  62  and FIG. 6 is a detailed view of the fuser/cooler module  68  of coating device  62 . Referring to FIGS. 4-7, modular coating device  62  includes an upper module  68  with components for coating the top of each sheet  42  and a lower module  70  with components for coating the bottom of each sheet  42 . Two print media paths are provided through post print finishing device  64 . A coating media path  44  runs through coating modules  68  and  70  and a bypass media path  45  bypasses coating modules  68  and  70 . Both media paths  44  and  45  discharge sheets  42  to an output tray  72  (shown in FIG. 7) or to other downstream finishing operations. 
     Upper module  68  includes a first/top side coating material web supply spool  12 , a first/top side web take-up spool  14 , and a first/top side fuser and cooler unit  74 . Lower module  70  includes a second/bottom side coating material web supply spool  16 , a second/bottom side web take-up spool  18 , and a second/bottom side fuser and cooler unit  76 . First/top side coating material web  20 , as shown in FIG. 5, runs from top supply spool  12  through fuser and cooler unit  74  to top take-up spool  14  around idler rollers  78  and  80 . Second/bottom side coating material web  24  runs from bottom web supply spool  16  through fuser and cooler unit  76  to bottom web take-up spool  18  around idler rollers  82  and  84 . Top supply and take-up spools  12 ,  14  and bottom supply and take-up spools  16 , 18  are positioned over one another to achieve a vertically compact design. 
     An exit drive roller  86  and associated pinch roller  88  propel media sheets  42  out of coating device  62  toward output tray  72 . Each of the rollers in upper coating module  68  are mounted to or otherwise supported by an upper module frame  90 . Each of the rollers in lower coating module  70  are mounted to or otherwise supported by a lower module frame  92 . FIG. 8 is a perspective view of upper module  68 . Module  68  and its counterpart lower module  70  are configured to slide into and out of post print finishing device  64  to facilitate installation, repair and replacement of the module. 
     The various components of coating device  62  may be directly supported by the frame, such as by mounting a component directly to the frame, or components may be indirectly supported by the frame, such as by mounting a component to a support structure or other component that is mounted to the frame. The frame that supports the components may be a module frame, as in upper module frame  90  and lower module frame  92 , an overall coating device frame, or the post print finishing device frame such as might be the case where the coating device is not constructed of modular units that slide into and out of the finishing device. 
     FIG. 9 illustrates a drive train for driven components of modular coating device  62 . In the drive train shown in FIG. 9, all of the major components in media path  44  and web paths  46  and  48  are driven by one motor. Other drive train configurations are possible and two or more motors could be used to drive the various components. Referring to FIG. 9, main drive stepper motor  94  drives main drive gear  96  clockwise. Bottom web take-up gear  98 , which is coupled to bottom web take-up spool  18 , is driven clockwise off main gear  96  through a spacer gear  100 . Top web take-up gear  102 , which is coupled to top web take-up spool  14 , is driven counter-clockwise off main gear  96  through a pair of reversing spacer gears  104  and  106 . Exit drive gear  108 , which is coupled to exit drive roller  86 , is driven counter-clockwise directly off main gear  96 . 
     Center drive gear  110 , which turns coaxially with main gear  96 , is driven clockwise at the urging of motor  94 . Top fuser roller gear  112 , which is coupled to top fuser roller  34 , and top cooler roller gear  114 , which is coupled to top cooler roller  56 , are driven counter-clockwise off center drive gear  110 . Bottom fuser roller gear  116 , which is coupled to bottom fuser roller  36 , and bottom cooler roller gear  118 , which is coupled to bottom cooler roller  58 , are driven clockwise off center drive gear  110  through a center spacer gear  120 . 
     Although not shown, the drive train illustrated in FIG. 9 may also include clutches interposed between some of the drive elements as necessary or desirable to maintain the appropriate relationship among moving parts. For example, electro-magnetic slip clutches should be included at take-up gears  98  and  102  to help control the tension on top and bottom coating webs  20 ,  20   a  and  24 ,  24   a.    
     While the present invention has been shown and described with reference to the foregoing exemplary embodiments, it is to be understood that other forms, details, and embodiments may be made without departing from the spirit and scope of the invention which is defined in the following claims.