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 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. A first peel bar is positioned immediately adjacent to the print media path, downstream from the fuser on the first side of the media path. A second peel bar is positioned immediately adjacent to the print media path downstream from the fuser and downstream from the first peel bar.

Description:
FIELD OF THE INVENTION 
     The invention is directed to print media coating devices and methods. 
     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 or provide a more uniform gloss level across the entire media (including both printed and unprinted 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 twice through the coating module of a post print finishing device—once to coat the top of the sheet and once to coat the bottom of the sheet. 
     The patent application filed on Oct. 25, 2002 under and entitled “Print Media Coating Device and Method” describes devices and methods for simultaneously coating both sides of printed media with a flexible film. For conventional single side coating, as well as the new two-side coating described in the &#39;897 patent application, it is desirable to use a peel bar to help separate the film carrier from the film after the film is applied to the media. Coatings are applied to print media by overlaying on the media a multilayered web containing the coating material and then applying heat and pressure to fuse the coating material to the media. The web includes a film/layer of coating material, a carrier (sometimes called a backing), and a release layer in between the coating material and the carrier. 
     In a conventional single side coating device such as the one illustrated in FIG. 11, the peel bar  2  protrudes slightly into media path  3  downstream from fuser  4  to apply pressure to coating material web  5 . Web  5  is threaded through fuser  4  from a supply spool  6  to a take-up spool  7 . Coating material web  5  and media sheet  8  are sandwiched together through fuser  4  with the coating material film part of web  5  facing sheet  8 . Fuser  4  applies heat and pressure to the web/sheet sandwich to affix the coating material film to the sheet  8 . The carrier portion of web  5  angles up off peel bar  2  to take-up spool  7 . The point pressure applied by peel bar  2  to web  5  helps the carrier portion of web  5  separate more cleanly from the coating film, now affixed to sheet  8 . 
     In one design of the new two-side coating device, the peel bars are placed directly opposite one another across the media path so that each carrier is peeled away from the coating film at the same time. During the development and testing of this design, it was discovered that the adhesion between the carrier and the coating film is such that each web tends to pull on the sheet as the carrier peels away from the coating film. This pull is not always the same on each side of the sheet. One side pulling harder than the other tends to relieve pressure on the weak side peel bar. This pressure relief can impede separation between the carrier and the coating film on the weak side which can, in turn, effect the quality of the coating film retained on that side of the sheet. Accordingly, the present invention was developed in an effort to maintain a more uniform pressure on each peel bar as a way to improve carrier/coating film separation. 
     SUMMARY 
     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. A first peel bar is positioned immediately adjacent to the print media path, downstream from the fuser on the first side of the media path. A second peel bar is positioned immediately adjacent to the print media path downstream from the fuser and downstream from the first peel bar. 
     Another embodiment of the invention is directed to a method for coating print media that includes: providing first and second coating material webs, each web having a coating material and a carrier carrying the coating material; sandwiching the print media between the first and second coating material webs; fusing coating material to the print media; and peeling the carrier from the coating material on the first coating material web and then peeling the carrier from the coating material on the second coating material web. 
    
    
     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 typical 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 and peel bars 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. 
     FIG. 10 is a detailed view of the peel bars shown in FIG.  6 . 
     FIG. 11 illustrates a conventional single side coating device. 
    
    
     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 , respectively and second/bottom side coating material supply and take-up spools  16  and  18 , respectively. 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 entitled “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. 
     Downstream from fuser  22 , 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. That is to say, top take-up spool  14 , top peel bar  52  and fuser  22  are positioned relative to one another such that web  20  bends around peel bar  52  on its way to top take-up spool  12 . Similarly, bottom take-up spool  18 , bottom peel bar  54  and fuser  22  are positioned relative to one another such that web  24  bends around bottom peel bar  54  on its way to bottom take-up spool  18 . Each web path  46  and  48  diverges from media path  44  at peel bars  52  and  54  at a sharp angle, preferably 60° to 130° and most preferably about 90°, to help carrier  30  separate more cleanly away from coating layer  28 . Peel bars  52  and  54  are not aligned directly opposite one another across the web/media path. Rather, one peel bar is positioned downstream from the other peel bar to help improve carrier/coating separation. 
     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 by 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  (FIG. 2) into sheet  42  to bond coating  28  to the top and bottom of the sheet  42  and softens release layer  32  to allow carrier layer  30  to be removed more easily from coating layer  28 . Spent webs  20   a  and  24   a , taken up on spools  14  and  18 , consist of carriers  30  and the remnants of release layers  32 . 
     In the coating device illustrated in FIG. 3, webs  20  and  24  and sheet  42  pass through a cooler  50  located downstream from fuser  22  and then 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 by take-up spools  14  and  18 . Cooler  50  cools webs  20  and  24  and sheet  42  to accelerate the curing of 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 cooler 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 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  53  and  54  at a sharp angle, preferably 60° to 130° and most preferably about 90°, to help carrier  30  separate 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 that 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. 
     In this staggered configuration, media sheet  42  reaches the upstream peel bar  54  where peeling carrier  30  from bottom web  24  is initiated at a first point in time. As sheet  42  reaches the downstream peel bar  52 , peeling carrier  30  from top web  20  is initiated at a second later point in time. 
     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  (output tray  72  is 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  runs from top supply spool  12  through fuser and cooler unit  74  to top take-up spool  14  around idler rollers  78  and  80  (web  20  is shown in FIG.  5 ). 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  (web  24  is shown in FIG.  5 ). 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  (output tray  72  is shown in FIG.  7 ). 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. 
     Referring now to FIGS. 6 and 10, top peel bar  52  is mounted to the housing  75  of top fuser/cooler unit  74 . Bottom peel bar  54  is mounted to the housing  77  of bottom fuser/cooler unit  76 . Each peel bar  52 ,  54  includes a web facing surface  53 ,  55  as shown in FIG.  10 . Rigid peel bars with a narrow line of contact against coating webs  20  and  24  are preferred. Hence, in the configuration shown in the drawings, web facing surfaces  53  and  55  are beveled away from the web enough that peel bars  52  and  54  contact the web only along a narrow edge  57 ,  59  on the downstream side of each peel bar  52 ,  54 , respectively. Because rigid housings can be used to stiffen an otherwise more flexible bar, mounting peel bars  52  and  54  to the fuser cooler unit housings  75  and  77  allows for more variability in the material used to construct peel bars  52  and  54  and the cross-sectional size of the peel bars. Alternatively, the peel bars could be constructed of rigid material having a sufficiently robust cross-section mounted on each end to. frames  90  and  92 . The peel bars could also be formed integral to housing  75  and  77 . Other suitable configurations that allow peel bars  52  and  54  to intercept webs  20  and  24  uniformly across the width of print media  42  are possible. 
     The distance along media path  44  between contact edges  57  and  59  of peel bars  52  and  54  and the extent to which peel bars  52  and  54  protrude into media path  44  may be adjusted as necessary or desirable for a particular operating environment. For example, in a typical business office documents are often printed on 24# paper with an inkjet or laser printer. A suitable web for coating such documents is nominally 12-15 μm thick and carries a 3.5-3.8 μm thick film of coating material. In this operating environment, the following spacing will provide suitable performance: approximately 30 mm between contact edges  57  and  59  of peel bars  52  and  54 , respectively and contact edges  57  and  59  protruding approximately 3 mm, into media path  44  with facing surfaces  53 ,  55  beveled away from a slightly radiused or flattened edge  57 ,  59 , respectively. A radiused or flattened edge  57 ,  59  is preferred to minimize the risk of cutting the web as it peels away from the paper or other print media. 
     Peel bars  52  and  54  are configured so that the two webs contact both peel bars at all times and so that the peel bars do not damage or impede media sheet  42 . The thickness and weight of media sheet  42  may vary significantly. When heavier media sheets  43  are coated, peel bars  52  and  54  may be spaced further apart and may protrude less into media path  44 . It is expected that in most operating environments, peel bars spaced apart 20-30 mm and protruding 2-5 mm into the media path will allow for the desired peeling. 
     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  through main gear  96 . 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 that is defined in the following claims.