Abstract:
A business form with a moisture transport accelerating and stabilizing coating for improving the transport of moisture through paper stock during printing in a laser printing. The coating improves the resistance of the paper to curling when heated in a laser printer and reduces the likelihood of paper jams, especially during duplex printing.

Description:
This application is a continuation-in-part of application Ser. No. 09/911,362, now U.S. Pat. No. 6,572,151 Jul. 23, 2001, the disclosure of which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a coating for paper, and more particularly, to a moisture transport accelerator and stabilizer coating for a label/form combination that is designed to allow the label/form combination to withstand the harsh environment of a laser printer during both simplex and duplex imaging processes. 
   One problem inherent in label/form construction is found in association with duplex imaging. For duplex printing in a laser printer, two passes through the fuser are made. The higher temperatures and increased dwell times can cause curling of the label/form combination, which can result in the label/form jamming the printer. This may be particularly problematic with respect to the use of short grain designed products where the bond paper is in a short grain direction in the printer. In the duplex imaging mode, the sheet needs to pass through the fuser twice, and significant temperatures can be generated. This can result in rapid loss of moisture by the heated sheet after its first pass through the fuser. Moisture gained in the bond portion of the structure escapes rapidly, causing the short grain sheet to curl and jam in the feed path, particularly in high humidity environments, where it may have absorbed additional moisture. 
   It is therefore an object of this invention to set forth a label/form combination assembly, which avoids the disadvantages and previously mentioned limitations of typical current document assemblies. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention, this is accomplished by providing a business form comprising: a sheet of laser printable stock; and a moisture transport accelerating and stabilizing coating on at least a portion of at least one side of the sheet of laser printable stock. 
   The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 
   BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic side view of the preferred embodiment of the completed construction of the label/form combination assembly; 
     FIG. 1A  is a schematic side view of an alternate embodiment of the completed construction of the label/form combination assembly; and 
     FIG. 2  is a plan view of the label/form combination assembly shown in  FIG. 1 . 

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in the FIGURES, a business form  5  according to an embodiment of the invention is comprised of a releasable label sheet  10  joined with a laser printable sheet  13 . Preferably, the laser printable sheet  13  is a short grain bond paper. The releasable label sheet  10  includes label stock  11  with a coating of pressure sensitive adhesive  14  on one side and a release stock  12  having a release coating  12   a  on the side engaging the pressure sensitive adhesive  14 . In a preferred embodiment, the non-coated side  12   b  of the release stock  12  is capable of being printed by a laser printer. The pressure sensitive adhesive  14  along one edge of the label stock  11  is left exposed, shown at  18 . A strip of cold bond adhesive  16  is applied to the non-coated side  12   b  of the release stock  12  adjacent the exposed pressure sensitive adhesive  18 . The cold bond adhesive  16  has characteristics to allow appropriate bonding between the sheets while not being subject to losing or altering the bonding characteristics when heat is applied in the printing process at the fusing station, either in simplex or duplex imaging. The preferred cold bond adhesive is a solventless, aqueous adhesive. A leading edge  22  of the laser printable sheet  13  is joined with the releasable label sheet  11  by both the applied cold bond adhesive  16  and the exposed pressure sensitive adhesive  18  at an overlap area  17 . 
   Joining the releasable label stock  11  and the laser printable sheet  13  in this manner yields two results: a thinner joint and a firmly anchored joint for simplex or duplex printing. Although the construction is effective in simplex printing, many of the advantages of the construction are particularly suited for duplex imaging. As previously explained, another problem associated with duplex printing, particularly with short grain paper, is curl. In duplex printing, the form needs to pass through the fuser twice. What commonly happens, especially in a high humidity environment, is the tendency for the form to curl after the first pass through the fuser. Moisture gained in the bond paper portion of the form escapes rapidly causing the short grain sheet to curl and jam in the feed path. To overcome this problem, a portion of the laser printable sheet  13  may be coated with a UV curable moisture transport accelerator and stabilizing coating  23  proximate a trailing edge  21  of the laser printable sheet  13 . This coating  23  is applied to at least one side of the laser printable paper  13  at its trailing edge  21  and preferably to both the face and the back of the laser printable paper  13 . There is no limit as to how much of the paper sheet can be coated. The entire laser printable sheet  13  can be coated with the moisture transport accelerator and stabilizing coating  23 . However, it is preferable that only a portion of the laser printable sheet  13  proximate the trailing edge  21  is coated. After the laser printable sheet  13  is coated with coating  23 , the coating is exposed to ultraviolet (UV) light to cure coating  23 . 
   Bond laser paper is designed to remain flat during its use in a laser printer. In a normal simplex imaging scenario, even a laser bond sheet will rapidly lose moisture as it is processed through a laser printer—which explains why some sheets curl after being imaged just once in the simplex mode. In a duplex mode, a standard laser bond that is short grain will curl as moisture is rapidly lost during its first fusing process. The coating  23  allows the sheet (at the area coated) to gain moisture at a more rapid rate after it has been exposed to the high heat of the fusing process of the first pass. What happens is the trailing edge  21  (which becomes the leading edge on the second pass) reaches equilibrium (flatness) faster than paper that has not been coated. In essence, the coating  23  acts as an accelerator for moisture gain in the sheet which allows the sheet to rapidly gain moisture back and thus achieve equilibrium (flatness) which allows it to process trouble-free through the next fusing stage of the duplex process. 
   The moisture transport accelerator and stabilizing coating  23  is a UV (ultraviolet) cured primer comprised of a mixture of:
         hexanediol diacrylate, a low viscosity, low volatility difunctional monomer having a hydrophobic backbone,   Ebecryl® 600 by UCB Chemicals, an acrylated epoxy oligomer, specifically bisphenol-A epoxy diacrylate,   trimethylolpropane triacrylate, a low viscosity, low volatility trifunctional liquid monomer, and       

   Irgacure® 651 by Ciba Specialty Chemicals Inc., a UV curable solid free-radical photoinitiator, specifically 2,2-dimethoxy-1,2-diphenylethan-1-one. 
   The UV primer  23  seals the fibers of the paper in the area primed without increasing the fiber thickness. This coating  23  prevents the absorption of moisture into the fibers yielding very open pores in the primed portion of the paper that allows quick passage of moisture through the paper. 
   If the primed surface is exposed to moisture, there is an initial curl toward the unexposed side of the paper; however, the coated paper fibers do not swell and moisture is quickly transported through the open pores of the paper. This results in an elevated state of equilibrium between the moisture and the paper and the curl quickly disappears—returning the paper to its original, flat state. 
   In comparison, a non-primed paper, when exposed to moisture, absorbs the moisture more slowly. This is due to the paper fibers swelling as they absorb moisture, thus causing the paper&#39;s pores to contract and consequently slowing the moisture passage through the paper. If moisture is exposed to the non-primed paper, the paper curls toward the unexposed side of the paper. Since the non-primed paper fibers swell, causing the pores to contract, moisture is slowly transported through the pores of the paper. The result is that equilibrium is achieved after a much longer time period compared to paper that has been primed with the UV coating  23 . 
   In the process of imaging a primed sheet of paper through a duplex laser printer, moisture in the paper is rapidly lost after being exposed to the elevated temperatures present in the fusing station. This rapid loss of moisture causes the paper to curl. As the sheet exits the fuser, the primer  23  allows moisture to be rapidly gained back into the primed sheet and achieve equilibrium—layflatness. This allows the sheet to continue on its process of entering the second imaging phase of duplex imaging. 
   The form  5  of the present invention is better suited for duplex printing in that the joint is more streamline for ease of feeding through the laser printer and the primary bond (cold glue) is resistant to the heat generated by the laser printer and therefore reduces the risk of the combined label/form failing apart at the joint. Further, the construction of this new joint may also be used for duplex printing with removable labels on both sides. The moisture transport accelerating and stabilizing coating  23  at the trailing edge of the laser printable paper  13  provides the dimensional stability required for trouble-free feeding through the paper path of the printer in a variety of printing environments, particularly high humidity conditions. 
   In addition to being used with label/form combinations, the moisture accelerating and stabilizing coating  23  can be used with other forms, both duplex and simplex, that are susceptible to curling during printing in a laser printer. 
   While the invention has been described in connection with specific embodiments thereof, it is clearly to be understood that this is done only by way of example and not as a limitation to the scope of the invention as set forth in the objects thereof and in the appended claims.