Abstract:
A coating composition, system, and method for printing documents that are difficult to chemically or physically forge and that are easy to visually verify are disclosed. The system includes a substrate, a toner, including a colorant and a dye, a coating including fluorescent material, e.g., a primary migration-enhancing coating, applied using an offset printing process and optionally a secondary migration-enhancing coating applied using an offset printing process. An image formed using the toner of the invention is readily verified by comparing a colorant-formed image and a dye-formed image and/or to a reverse negative imaged formed by the dye quenching the fluorescent material. In addition, if a solvent is used in an attempt to alter the printed image on the substrate, the dye migrates or diffuses to indicate tampering with the document.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of application Ser. No. 12/543,438, entitled, COATING COMPOSITION, SYSTEM INCLUDING THE COATING COMPOSITION, AND METHOD FOR PRODUCING SECURE IMAGES, filed Aug. 18, 2009, which claims the benefit of Provisional Application No. 61/139,510, entitled A SYSTEM AND METHOD FOR PRODUCING A SECURE DOCUMENT USING TONER-BASED IMAGING, filed Dec. 19, 2008; this application also claims the benefit of Provisional Application No. 61/253,471, entitled METHOD AND APPARATUS FOR PRODUCING OVERT AND COVERT SECURITY IMAGES ON PAPER, filed Oct. 20, 2009; the entire disclosures of which are hereby incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to compositions, systems, and methods for printing documents. More particularly, the invention relates to an improved coating composition for printing documents in a secure manner, such that the documents are difficult to forge and original versions of the documents are readily verifiable, and to a system including the coating composition and to methods of using and making the coating composition. 
       BACKGROUND OF THE INVENTION 
       [0003]    Toner-based imaging, which generally involves forming an electrostatic or magnetic image on a charged or magnetized photoconductive plate or drum, brushing the plate or drum with charged or magnetized toner, transferring the image onto a substrate such as paper, and fusing the toner onto the substrate using heat, pressure, and/or a solvent, can be used to form relatively inexpensive images on a surface of a substrate. 
         [0004]    Because toner-based imaging, such as printing, is a relatively quick and inexpensive technique for producing copies of images, the technique is often employed to produce documents that were traditionally formed using other forms of printing or imaging—e.g., impact printing or ink-jet printing. For example, in recent years, toner-based imaging has been employed to produce financial documents, such as personal checks, stocks, and bank notes; legal documents such as wills and deeds; medical documents such as drug prescriptions and doctors&#39; orders; and the like. Unfortunately, because the image is formed on the surface of the substrate, documents produced using toner-based imaging techniques may be relatively easy to manipulate, forge and/or duplicate. 
         [0005]    Various techniques for printing or forming secure documents have been developed over the years. For example, U.S. Pat. No. 5,124,217, issued to Gruber et al. on Jun. 23, 1992, discloses a secure printing toner for electrophotographic processing. This toner, when exposed to a solvent such as toluene, often used in document forgery, produces a color stain indicative of the attempted forgery. This toner is only useful to disclose an attempted forgery when a particular solvent is used to remove a portion of a printed image. Thus, the toner cannot be used to mitigate copying of the document or forgery resulting from adding material to the document. 
         [0006]    U.S. Pat. No. 5,714,291, issued to Marinello et al. on Feb. 3, 1998, discloses another toner that includes submicron ultraviolet sensitive particles. A document printed with the toner can be authenticated using ultraviolet light. 
         [0007]    Other techniques for producing secure images include modifying the paper onto which the image is printed. Such modified papers may include paper having a low-ink-absorption coating and paper including crushable micro capsules that contain leuco ink and a color acceptor. Although techniques including these forms of paper work relatively well for impact-type printing or copying, the techniques would not work well in connection with toner-based or similar printing methods. 
         [0008]    Other techniques for producing secure images include providing special paper coatings to increase smudge resistance of an image created by an electrostatic process. However, the coatings generally do not affect an ability to add material to the document or authenticate the originality of the document. 
         [0009]    For the foregoing reasons, improved compositions, methods and apparatus for forming secure documents using toner-based processing, which are relatively easy and inexpensive, are desired. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an improved coating composition, system and method for producing secure documents. Various ways in which the present invention addresses the drawbacks of the prior art are addressed below. In general, however, the coating composition, system, and method of the present invention produce images that are difficult to alter and that are relatively easy to assess whether an alteration to a printed image has been attempted or made. 
         [0011]    In accordance with various embodiments of the invention, a system includes a substrate, a toner that includes a colorant and a dye applied to a surface of the substrate, and a coating including fluorescent material. In accordance with exemplary aspects of these embodiments, the coating including fluorescent material is a primary migration-enhancing coating. As set forth in more detail below, the primary migration-enhancing coating may be configured to facilitate migration of the dye through the substrate to form an image visible from a second surface of the substrate. In accordance with additional and/or alternative aspects of these embodiments, the system further includes a secondary migration-enhancing coating, which may additionally and/or alternatively include fluorescent material. The secondary coating may be configured as a barrier between the first coating and other substrates and/or to minimize effects of different substrates. In accordance with further aspects of these embodiments, the toner is applied using a laser printer. And, in accordance with yet additional aspects, the coating comprising fluorescent material, the primary migration-enhancing coating and/or secondary migration-enhancing coating is applied using an offset printing process. As discussed in more detail below, using an offset printing process to apply the coating comprising fluorescent material, the primary migration-enhancing coating and/or secondary migration-enhancing coating allows for application of the coating(s) to select areas of the substrate—within the registration of the printer. 
         [0012]    In accordance with additional embodiments of the invention, a coating composition, e.g., a composition for application of a primary migration-enhancing coating, used for producing secure images, includes an oil, a resin, an anti-misting agent, an anti-offsetting agent, and fluorescent material. In accordance with various exemplary aspects, the primary coating composition is configured for application to a substrate using offset printing. 
         [0013]    In accordance with yet additional embodiments of the invention, a coating composition, e.g., a composition for application of a secondary migration-enhancing coating, includes a high viscosity oil with low surface tension, an anti-misting agent, and optionally fluorescent material. In accordance with various aspects of these embodiments, the secondary migration-enhancing coating composition includes a plurality of oils. In accordance with further exemplary aspects, the secondary coating composition is configured for application to a substrate using offset printing. 
         [0014]    In accordance with yet further embodiments of the invention, a method of forming a secure document includes the steps of providing a substrate, applying a colorant and a dye to the substrate, and applying a coating including fluorescent material (e.g., a primary migration-enhancing coating, which includes fluorescent material) to the substrate using, for example, an offset printing (e.g., offset lithography) process. In accordance with various aspects of these embodiments, the process further includes the step of applying a secondary migration-enhancing coating, which may optionally include fluorescent material. In accordance with further aspects, the secondary migration-enhancing coating is applied using offset printing techniques. As set forth in more detail below, the colorant and dye, the coating including fluorescent material, the primary migration-enhancing coating, and the secondary migration-enhancing coating may be applied to the same surface of the substrate, or the colorant and dye may be applied to a first surface of the substrate and the coating including fluorescent material, the primary migration-enhancing coating, and/or the secondary migration-enhancing coatings may be applied to a second surface of the substrate. 
         [0015]    In accordance with additional embodiments of the invention, a method of forming a secure document includes the steps of providing a substrate, applying a colorant and dye to the substrate, applying a primary migration-enhancing coating to the substrate, and applying a secondary migration-enhancing coating overlying the primary migration-enhancing coating. In accordance with various aspects of these embodiments, the primary migration-enhancing coating includes fluorescent material and is applied using, for example, offset printing techniques. In accordance with further aspects, the secondary migration-enhancing coating is applied using offset printing techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more complete understanding of the present invention may be derived by referring to the detailed description and claims, considered in connection with the figures, wherein like reference numbers refer to similar elements throughout the figures, and: 
           [0017]      FIG. 1  illustrates a secure document system in accordance with various embodiments of the invention; 
           [0018]      FIGS. 2A-2C  illustrate a first surface and a second surface of a secure document in accordance with exemplary embodiments of the invention; 
           [0019]      FIG. 3  illustrates an offset printing station for use with various embodiments of the invention; and 
           [0020]      FIG. 4  illustrates an offset printing apparatus, including multiple stations, for use with various embodiments of the invention. 
       
    
    
       [0021]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
       DETAILED DESCRIPTION 
       [0022]    The following description is provided to enable a person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventors of carrying out their invention. Various modifications to the description, however, will remain readily apparent to those skilled in the art, since the general principles of a coating composition, system, and method for forming secure images on a document have been defined herein. 
         [0023]    The present invention may be used in connection with a variety of printing processes, and is particularly well suited for electrophotography and offset printing applications. The following description describes a coating composition, system, and method to produce secure documents using electrophotography and lithographic offset processes. However, the invention is not limited to such composition, system, or process. 
         [0024]    Exemplary coatings and systems in accordance with various embodiments of the invention may be used for a variety of purposes, such as to produce financial documents, such as personal checks, stocks, and bank notes; legal documents such as birth certificates, drivers&#39; licenses, wills, and deeds; medical documents such as drug prescriptions, transcripts, and doctors&#39; orders; educational documents, such as transcripts and records, and the like. 
         [0025]    FIGS.  1  and  2 A- 2 C illustrate a system  100 , which includes a substrate  102 , a toner  104 , a first or primary migration-enhancing coating  106 , including fluorescent material  116  (the coating containing fluorescent material in this illustrative example), a second or secondary migration-enhancing coating  108 , and a dye  110 . Although system  100  is illustrated with multiple coatings, as discussed in greater detail below, systems in accordance with alternative embodiments may include fewer coatings or layers, wherein, for example, a single coating may include the attributes of one or both coatings  106  and  108 . Furthermore, although coatings  106 ,  108  are illustrated as being directly opposite toner  104  on a second surface  114  of substrate  102 , coatings  106  and/or  108  could alternatively be disposed on the same surface as and underlying toner  104 , and in either case, need not be directly corresponding to a location of toner  104 . Furthermore, while illustrated with coating  106  including fluorescent material, coating  108  or another layer may additionally and/or alternatively include fluorescent material; when coating  108  or another layer includes fluorescent material, coating  108  or the other layer is referred to as the coating including fluorescent material. 
         [0026]    Toner  104  and dye  110  function together with coatings  106  and  108  to provide a first image  202  using toner  104  on a first surface  112  of substrate  102  and a latent image  204  with dye  110  that may be visible from first surface  112  and/or a second surface  114 . In accordance with specific examples of the invention, dye  110  and fluorescent material  116  function together to produce a reverse negative image  206  within an area coated with the fluorescent coating (e.g., coating  106 ). When viewed under a fluorescing light, e.g., ultraviolet light, a reverse negative image may be formed by, for example, dye  110  quenching fluorescent material  116 . 
         [0027]    In accordance with various embodiments of the invention, the secure image systems (e.g., system  100 ) are difficult to forge and copies of the secure images are easily detected, because any mismatch between the printed image (e.g., image  202 ) and the latent image (e.g., image  204 ) and/or reverse negative image (e.g., image  206 ) indicates an alteration or attempted alteration and a missing latent image and/or reverse negative image is indicative of a copy of the document. 
         [0028]    System  100  may be formed by applying a toner and a dye onto substrate  102  using, for example, an electrostatic or electrophotographic process, such as a laser printing process and applying coating  106  and/or coating  108  using rod, gravure, spray, or wet or dry offset printing process (e.g., a lithographic process). Using an offset printing process to apply coatings  106  and/or  108  is advantageous because it allows the coating to be applied relatively inexpensively and, if desired, allows for precise application of the coatings only to desired areas of the substrate—within the precision of the register of the lithographic printer. In accordance with one embodiment of the invention, toner  104 , including dye  110 , is printed onto a first surface of a substrate and one or more coatings  106 , 108  are applied onto a second surface of the substrate. In accordance with alternative embodiments, coatings  106 ,  108  may be applied onto a first surface of the substrate and subsequently a toner-based image may be printed on top of the coating(s). 
         [0029]      FIG. 3  illustrates a station and  FIG. 4  illustrates an apparatus including multiple stations for application of coating  106  and/or  108  using offset printing, in accordance with various embodiments of the invention. Exemplary station  300  includes an ink or composition transfer system  302 , a damping station  304 , a plate cylinder  306 , an offset cylinder  308 , and an impression cylinder  310 . 
         [0030]    In accordance with various embodiments of the invention, during operation of station  300 , a coating (e.g., coating  106 ) is applied to a substrate  320 , such as paper, by first applying water from system  304 , and then a coating composition from system  302 , onto cylinder  306 , using roller  316  and rollers  312 - 314 , respectively. The coating composition and the water are immiscible, such that the water repels the coating composition from the non-image areas of cylinder  306  and the coating composition is applied to image areas of cylinder  306 . The coating composition from cylinder  306  is then transferred to offset cylinder  308 , which in turn, is used to transfer the coating composition to substrate  320 . Coating  108  may be applied in the same manner. As noted above, applying coating compositions in this manner allows for very precise application of the coating compositions, which may be desirable to, for example, reduce an amount of coating material used to form system  100  and to mitigate unwanted diffusion of dye  110 . 
         [0031]    Apparatus  400  may be used to provide multiple images and/or coatings to a substrate using offset techniques. Apparatus  400  includes multiple stations  402 ,  404 , and  406 , each station generally including an ink or coating composition transfer system  302  to transfer an image or coating composition onto a substrate. By way of example, an image can be transferred to a substrate (e.g., substrate  102 ) using station  402 . Station  404  is then used to apply layer or coating  106  onto substrate  102 . Coating  106  may be applied substantially in register with and on an opposite surface with toner  104 , as illustrated, or underlying toner  104 . Similarly, if used, coating  108  can be applied overlying coating  106 . 
         [0032]    Referring back to  FIG. 1 , in accordance with various embodiments of the invention, substrate  102  may include any suitable material onto which an image can be transferred. Exemplary substrate  102  materials include paper (e.g., 20 lb. MOCR bond paper), and other substrates suitable for offset lithographic printing. 
         [0033]    Toner  104  may include any suitable composition capable of printing an image on a surface of substrate  102 . In accordance with various embodiments of the invention, toner  104  includes a thermoplastic binder resin, a colorant, a charge-controlling agent, and a migrating dye  110 . Each of the thermoplastic binder resin, the colorant, release agent, and the charge-controlling agent may be the same as those used in typical toners. The toner may be a one-component toner or a multiple-component toner (e.g., toner and developer). 
         [0034]    The thermoplastic binder resin helps fuse the toner to the substrate. In accordance with one embodiment of the invention, the binder resin has a melt index of between about 1 g/10 min. and 50 g/10 min. at 125° C. and has a glass transition temperature between about 50° C. and about 65° C. Exemplary materials suitable for the thermoplastic binder resin include polyester resins, styrene copolymers and/or homopolymers—e.g., styrene acrylates, methacrylates, styrene-butadiene-epoxy resins, latex-based resins, and the like. By way of particular example, the thermoplastic binder resin is a styrene butadiene copolymer sold by Eliokem as Pliolite S5A resin. 
         [0035]    The colorant for use with toner  102  can be any colorant used for electrophotographic image processing, such as iron oxide, other magnetite materials, carbon black, manganese dioxide, copper oxide, and aniline black. In accordance with one particular example, the colorant is iron oxide sold by Rockwood Pigments as Mapico Black. 
         [0036]    The charge-control agent helps maintain a desired charge within the toner to facilitate transfer of the image from, for example, an electrostatic drum, to the substrate. In accordance with one embodiment of the invention, the charge control agent includes negatively-charged control compounds that are metal-loaded or metal-free complex salts, such as copper phthalocyanine pigments, aluminum complex salts, quaternary fluoro-ammonium salts, chromium complex salt type axo dyes, chromic complex salt, and calix arene compounds. 
         [0037]    The toner may also include a releasing agent such as a wax. The releasing agent may include low molecular weight polyolefins or derivatives thereof, such as polypropylene wax or polyethylene wax or a copolymer of polypropylene wax and polyethylene wax. 
         [0038]    Preferred dyes in accordance with the present invention exhibit a strong color absorbance through a substrate (e.g., substrate  102 ), good solubility in a migration fluid, good stability, do not adversely affect photographic development properties of the toner, are compatible with the toner resin, do not separate or bloom, are non toxic, and dissolve and/or migrate in polar and/or non-polar solvents used to attempt document forgery—e.g., by attempting to remove an image from the top surface of the substrate. Exemplary polar solvents used in such attempted forgery include acetone, methanol, methyl ethyl ketone, and ethyl acetate; exemplary non-polar solvents include toluene, mineral spirits, gasoline, chloroform, heptane, and diethyl ether. In addition, the dyes are preferably indelible. 
         [0039]    Exemplary soluble dyes, suitable for use as dye  110 , include phenazine, stilbene, nitroso, triarylmethane, diarlymethane, cyanine, perylene, tartrazine, xanthene, azo, disazo, triphenylmethane, fluorane, anthraquinone, pyrazolone quinoline, and phthalocyanine, or derivatives thereof. In accordance with one embodiment of the invention, the dye is red in color and is formed of xanthene, sold by BASF under the trade name Baso Red 546. In accordance with another embodiment of the invention, the dye is red in color and is formed of disazo, and sold under the name Bright Red LX-5988 from Pylam Products Company, Inc. In accordance with yet another embodiment of the invention, the dye is blue in color and is formed of anthraquinone, sold under the name Bright Blue LX-9224 by Pylam Products Company, Inc. Other color dyes of similar chemical structure are also suitable for use with this invention. 
         [0040]    The following example illustrates a composition that may be used to form a toner e.g., toner  104 . The example set forth below is merely illustrative, and it is not intended that the invention be limited to this illustrative example. 
       Example 1 
       [0041]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Mixture of styrene acrylic and 
                 51 
               
               
                   
                 polyester polymers 
               
               
                   
                 mixture of iron oxides 
                 40 
               
               
                   
                 polyethylene wax 
                 5 
               
               
                   
                 chromium complex 
                 2 
               
               
                   
                 Pylam Bright Red LX-5988 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0042]    A toner of example 1 was prepared by melt mixing the components on a two-roll mill, jet milling the composition, and classifying the mixture to about 11 microns and blending the mixture with about 1% mixture of silicas. The toner was tested using a Hewlett-Packard 4050 laser printer and exhibited the desired properties. 
         [0043]    In accordance with various embodiments of the invention, coating  106  includes a migration-enhancing agent configured to assist dye  110  to migrate through at least a portion of substrate  102 . Coating  106  may be applied in neat form, without additional diluents, or may include additional diluents. In accordance with various aspects of these embodiments, coating  106  includes an oil as a migration-enhancing agent, a resin, and an anti-misting agent, such as silica, bentonite clay, kaolin, titanium dioxide, or any combination thereof. The anti-misting agent mitigates unwanted spray of coating material. The oil may be a single-component oil or include multiple components, such as oils, plasticizers, liquid polymers, and combinations thereof. The migration fluid may alternatively and/or additionally be adsorbed onto a carrier, such as silica. The migration fluid may also additionally and/or alternatively be encapsulated by a shell that can rupture—e.g., during a printer fusing process. The migration fluid may also be used with additional coating components. For example, the migration fluid may be sealed with the paper sheet by a coating material, such as a polymer, or the like. The additional coating component may be included with the migration fluid or may be added during another coating step. By way of example, the oil may include one or more of the following compounds: benzyl butyl phthalate, bis (2-ethylhexyl) adipate, trioctyl trimellitate, and 2,2,4-trimethyl-1,3-pentanediol diiosbutryate. The resin may be a phenolic modified rosin ester or other resin or compound, yielding high viscosity (e.g., greater than about 70,000 cp) and low tack and low misting properties, such as Sylvaprint 87-85 available from Arizona Chemical. 
         [0044]    In accordance with further aspects of these embodiments, coating  106  includes an anti-offsetting agent, such as silica, pea starch, wheat starch, silicone oil, a wax, or any combination thereof. The wax may be a synthetic wax, such as fluorocarbon wax, polyethylene, polypropylene, combinations thereof, or a natural wax, such as carnauba wax, or a combination of natural and synthetic waxes. In accordance with further aspects, a particle size of the anti-offsetting agent may range from about 0.2 microns to about 25 microns or about 10 to about 25 microns. 
         [0045]    As noted above, an exemplary coating  106  may also include fluorescent material. The fluorescent material may be material (e.g., dye or pigment) visible under ambient light and/or may become visible under other radiation, e.g., ultraviolet radiation. The fluorescent material may fluoresce any suitable color, such as fluorescent white, fluorescent yellow, fluorescent yellow green, fluorescent green, fluorescent blue, fluorescent orange, fluorescent red, or fluorescent pink. In accordance with various examples of the invention, the fluorescent material also becomes quenched (i.e., does not fluoresce) by dye  110 , when dye  110  contacts fluorescent material  116 . 
         [0046]    In accordance with further embodiments of the invention, a composition for application of coating  106  (e.g., a composition of a solution for station  302 ) includes about 25% to about 90%, about 35% to about 80%, or about 50% to about 75% oil; about 10% to about 60%, or about 20% to about 50%, or about 30% to about 40% resin; and about 0.1 % to about 10%, or about 0.02% to about 5%, or about 0.5% to about 4% anti-misting agent. In accordance with various aspects of these embodiments, the composition includes about 0.1% to about 10%, or about 0.2% to about 5%, or about 0.5% to about 4% anti-offsetting agent and various combinations of these compounds. When coating 106 includes fluorescent material, the composition includes about 0.1% to about 10%, or about 0.3% to about 6%, or about 0.5% to about 4% fluorescent material. All percents set forth herein are in weight percent unless otherwise noted. 
         [0047]    The following non-limiting examples illustrate various combinations of materials and processes useful in forming a coating composition in accordance with various embodiments of the invention. 
       Example 2 
       [0048]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Oil 
                 64% 
               
               
                   
                 Resin 
                 33% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                 Pea Starch 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0049]    A composition for coating  106  was prepared by first heating a stirred mixture of the oil and the silica (e.g., Syloid Rad 2105 available from Grace Davidson) until a temperature of about 250° F. was reached. While continuing to increase the temperature of the mixture, the resin was slowly added to the mixture. After all the resin has been added and the temperature had reached about 320° F. and had not exceeded about 360° F., the mixture is held at about 360° F. until all of the resin is dissolved. The mixture was then allowed to cool to a temperature below about 135° F., and then the pea starch was added. The mixture was mixed until the pea starch (e.g., pea starch available from Nutri-Pea Limited) was fully dispersed. 
         [0050]    After the mixture had cooled to about 70° F., the viscosity of the mixture was measured with a falling rod viscometer. The viscosity of the composition at about 70° F. was between about 40,090 cps and 95,000 cps. The coating was applied to the paper with an offset press (e.g., using station 302). The amount of coating applied was in the range of about 0.3 mg/sq. inch to about 4 mg/sq. inch. 
       Example 3 
       [0051]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Oil 
                 64% 
               
               
                   
                 Resin 
                 33% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                 Wax 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0052]    Another composition for application of coating  106  was prepared by first heating a stirred mixture of the oil, the wax, and the silica until a temperature of about 250° F. was reached. While continuing to increase the temperature of the mixture, the resin was slowly added to the mixture. After all the resin had been added and the temperature had reached about 320° F. but had not exceeded 360° F., the mixture was held at about 360° F. until all of the resin was dissolved. The mixture was mixed until the pea starch was fully dispersed. 
         [0053]    After the mixture had cooled to about 70° F., the viscosity of the mixture was measured with a falling rod viscometer. An exemplary viscosity was between about 40,000 cps and 95,000 cps at about 70° F. The coating was applied to the paper with an offset press. The amount of coating applied was in the range of about 0.3 mg/sq. inch to about 4 mg/sq. inch. 
       Example 4 
       [0054]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Oil 
                 64% 
               
               
                   
                 Resin 
                 33% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                 Wax 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0055]    Yet another composition for application of coating  106  was prepared by first heating a stirred mixture of the oil, the wax and the silica until a temperature of about 250° F. was reached. The silica was a large particle size silica (e.g., about 9.0 microns) such as Sylysia 380, available from Fuji Sylysia Chemical Ltd. While continuing to increase the temperature of the mixture, the resin was slowly added to the mixture. 
         [0056]    After all the resin had been added and the temperature had reached about 320° F. but not exceeded 360° F., the mixture was held at about 360° F. until all of the resin dissolved. The mixture was allowed to mix until the pea starch was fully dispersed. 
         [0057]    After the mixture had cooled to about 70° F., the viscosity of the mixture was measured with a falling rod viscometer. An exemplary viscosity is between about 40,000 cps and 95,000 cps at about 70° F. The coating was applied to the paper with an offset press. The amount of coating applied was in the range of about 0.3 mg/sq. inch to about 4 mg/sq. inch. 
       Example 5 
       [0058]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Oil 
                 62% 
               
               
                   
                 Resin 
                 35% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                 Pea Starch 
                 1% 
               
               
                   
                 Fluorescent Dye 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0059]    The substrate coating of Example 5 was prepared by heating a stirred mixture of the oils and the silica until a temperature of about 250° F. was reached. While continuing to increase the temperature of the mixture, the resin is slowly added to the mixture. After all of the resin has been added and the temperature has reached about 320° F. but not exceed about 360° F., the mixture is held at about 360° F. until all of the resin has dissolved. The mixture is then allowed to cool and at a temperature below 135° F., the pea starch and D043 fluorescent dye from DayGlo Color Corp. is added. The mixture is stirred until the pea starch is fully dispersed. 
         [0060]    After the mixture has cooled to about 70° F., the viscosity is measured with a falling rod viscometer. Once the viscosity falls into a range of about 40,000 cp to about 95,000 cp at about 70° F., the coating was applied to the paper with an offset press. The amount of coating applied was in the range of about 0.3 mg/sq. inch to about 4 mg/sq. inch. 
         [0061]    As noted above, systems in accordance with various embodiments of the invention include a secondary migration-enhancing coating  108 , which may be applied overlying coating  106 . In accordance with various aspects, the composition for forming coating  108  includes a high viscosity oil (e.g., viscosity about or greater than about 100,000 cp) having a low surface tension and an anti-misting agent. The oil may be a single oil (e.g., a high-viscosity silicone oil) or a combination of oils (e.g., silicone oils) having different viscosities, such that the final viscosity of the composition is suitable for offset printing. The anti-misting agent may include any of the anti-misting agents noted above. 
         [0062]    In accordance with further embodiments of the invention, a composition for application of coating  108  (e.g., a composition of a solution for station  302 ) includes about 70% to about 99.9%, about 85% to about 99.5%, or about 95% to about 99% of a first silicone fluid; and about 0.1 to about 30%, or about 0.2% to about 15%, or about 0.5% to about 2% silica. In accordance with various aspects of these embodiments, the composition includes about 0% to about 50%, or about 10% to about 30%, or about 15% to about 25% of a second silicone fluid. Exemplary first silicone fluids include moderately-high (10,000±5000 cp) to high viscosity (about 100,000 cp) di-methyl silicones fluids, and exemplary second silicone fluids include extremely high (about 1 million cp) viscosity di-methyl silicones fluids. In accordance with further exemplary embodiments of the invention, a composition for application of coating  108  includes fluorescent material. The composition may include about 0.1% to about 10%, or about 0.3% to about 6%, or about 0.5% to about 4% fluorescent material. 
         [0063]    The following examples illustrate compositions that may be used to form a secondary migration-enhancing coating—e.g., coating  108 . 
       Example 6 
       [0064]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Silicone Fluid 
                 98% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                 Fluorescent Dye 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0065]    A secondary migration-enhancing coating according to this example was made by weighing a desired amount of high viscosity silicone oil such as a di-methyl silicone (e.g., DM Fluid 100,000, sold by Shin-Etsu Chemical) and a five micron silica powder into a vessel equipped with a stirrer. The solution was stirred until a uniform dispersion was obtained. The mixture can be heated to facilitate the mixing. After the mixture was well dispersed and cooled, the viscosity was measured. An exemplary viscosity range for the composition is between about 54,000 cps and about 100,000 cps at a temperature of about 70° F. The coating was applied via an offset printing press utilizing a station subsequent to the station used to apply coating  106 . The amount of coating applied was in the range of about 0.2 mg/sq. inch to about 6 mg/sq. inch. 
       Example 7 
       [0066]      
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Extremely High Viscosity Silicone Fluid 
                 25% 
               
               
                   
                 Moderately High Viscosity Silicone Fluid 
                 74% 
               
               
                   
                 Silica 
                 1% 
               
               
                   
                   
               
             
          
         
       
     
         [0067]    A secondary migration-enhancing coating according to this example was made by weighing a desired amount of extremely high viscosity silicone oil such as a di-methyl silicone (e.g., oil having a viscosity of about 1 million cp or more, such as DM Fluid 1,000,000, sold by Shin-Etsu Chemical), moderately high viscosity silicone oil, such as a lower molecular weight di-methyl silicone (e.g., oil having a viscosity of about 10,000±5000 cp, such as DM Fluid 10,000, sold by Shin-Etsu Chemical), and a five micron silica powder into a vessel equipped with a stirrer. The solution was stirred until a uniform dispersion was obtained. The mixture can be heated to facilitate the mixing. After the mixture was well dispersed and cooled, the viscosity was measured. An exemplary viscosity range for the composition was between about 54,000 cps and about 100,000 cps at about 70° F. The coating was applied via an offset printing press utilizing a station subsequent to the station used to apply coating  106 . The amount of coating applied was in the range of about 0.2 mg/sq. inch to about 6 mg/sq. inch. 
         [0068]    Documents were printed in accordance with examples 1-4 and 6-7 described above using a Hewlett Packard Laserjet 4250 printer. Initially, the resulting image had high optical density, high resolution with no noticeable background, and no migration of the visible red dye was apparent. Within 24 hours, areas of printed toner were removed from the surface of the paper and it was observed that red residual images had started to work into the paper. Within 72 hours of printing, an indelible image became visible on the non-printed side of the paper. This measurement can be qualified by measuring the reflective optical density difference between the image on the second surface of the substrate and the non-image area on the second surface of the substrate. In accordance with various exemplary embodiments of the invention, an optical density difference of at least 0.07 optical density units measured 72 hours after the first side of the substrate has been printed with a laser printer is observed. 
         [0069]    Documents were also printed with the coatings of examples 1, 5 and 6, using a Hewlett Packard Laserjet 4015 printer to print an image on a first surface of a substrate and using offset printing techniques to apply coating  106 ,  108  to the second surface of the substrate. Initially, the resulting image had high optical density, high resolution with no noticeable background, and no migration of the visible red dye was apparent. After printing an image on a first surface of a substrate, the coating including fluorescent material (e.g., coating  106 ) is visible from the other side of the document. After about twenty-four hours have elapsed since applying the toner, the toner image is visible on the first surface, and a red indelible image of the printed image is visible from the second surface. The fluorescent material is visible under fluorescent light. However, in areas where the indelible image has migrated to the fluorescent material, the fluorescent material is quenched, causing an inverse negative indelible image under ultraviolet light. 
         [0070]    Although the present invention is set forth herein in the context of the appended drawing figures, it should be appreciated that the invention is not limited to the specific form shown. For example, while the invention is conveniently described in connection with electrostatic printing and offset printing, the invention is not so limited; the toner of the present invention may be used in connection with other forms of printing—such as iongraphic, magnetographic, rod, gravure, spray, and similar techniques. Various other modifications, variations, and enhancements in the design and arrangement of the composition, method, and system set forth herein may be made without departing from the spirit and scope of the present invention as set forth in the appended claims.