Abstract:
A method for creating and transferring digitally created images on a film to a target surface via heat and/or pressure transfer using a modified large-format digital printer. The method generally comprises the steps of modifying a large-format digital printer to convert it from heat fused toner printing to cold toner printing, preparing a transfer film, creating a digital image, applying a release layer onto the transfer film, printing the image onto the release layer on the transfer film in a reverse mirror-image manner, applying an adhesive overtop said image, and pressure transferring the image onto the target substrate and peeling away the transfer film to selectively leave the image on the target substrate. The present method results in a cleaner, clearer more eye-catching graphic deposited in a more robust, wear-tolerant manner on a wider variety of substrates including rough and porous materials such as leather.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     The present application derives priority from U.S. Provisional Application Serial No. 60/831,838 filed 19 Jul. 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to digital printing and, more specifically, to a method for transferring digitally created images from film to a target surface via heat and/or pressure transfer.  
         [0004]     2. Description of the Background  
         [0005]     Traditional offset printing processes involve a number of expensive and time-consuming steps, such as plate imaging and mounting. A number of manufacturers are now selling digital printers that print documents directly from electronic files to paper, or a variety of other substrates. These digital printers greatly simplify the printing process. Other than buying a digital printer and preparing a design to be printed, there are no other start-up costs or steps involved in the digital printing process. Thus, these printers allow cost-effective high quality shorter print runs. Both the form and content of each consecutive print can be different. Currently, only digital printing technology can provide the level of personalization and customization demanded by many manufacturers.  
         [0006]     Current purveyors of digital printing equipment include Xeikon, Kodak, Dotrix, HP and Xerox. Xeikon in particular targets the high-end segment of the digital printing market with printing presses that deliver excellent print quality and cost-effectiveness. Xeikon caters to an “on demand” business model, print shops that cater to customers who order large quantities of color documents that require delivery by the next day. The Xeikon digital printer, in combination with the Xeikon Digital Front End software, offers a print quality with superb color matching and perfect front to back registration. The result is a consistent high-quality, full-color print with astounding richness and depth of color that sets the standard for the rest of the market.  
         [0007]     The Xeikon print series are configured for successive application of four colors plus white, if required, to a medium as it travels across the printing cylinders. When printing to a 4 color-process toner based output printing system, there are four colors (Cyan, Magenta, Yellow, and Black, the combinations of which recreate any photograph or color in a desired spectrum. For example, a full color photograph of a child in a red dress would be broken down into millions of small pixels-each pixel has a 4-color value assigned to it. A pixel that is in the position in the child&#39;s face would have a value of Cyan-5%, Magenta-42%, Yellow-34%, and Black-10%. The typical shade of black will be Cyan-75%, Magenta-68%, Yellow-67%, and Black-90%. In a five color press a fifth color can be used as a specialty toner color or white. For example, a layer of white can be applied as the fifth color to enhance the colors and give the print opacity. This way, the substrate doesn&#39;t show through the image. There is the potential for even more colors or additional specialty toners simply  
         [0008]     In a conventional direct electrostatic color printing system, a plurality of rotating cylinders are statically charged by charging electrodes, and LEDs remove the charge selectively according to a color-separated pattern. The pattern is typically generated by the front end of the print engine taking the image file sent to the front ends and converting into a digital format that the engine will print The color-separated pattern is then imparted to the surface of the respective cylinders by the cylinder being completely charged with static charge and the this charge being removed by exposure to LEDs as the cylinder rotates past these LEDs. The LEDs are switched on and off according to the pattern required. The charged cylinders continue to rotate past a toner applicator that deposits toner on the pattern. Toner is attracted and transferred, according to the charged pattern or image, from the toner applicator onto the cylinder. Next, a print media is run across the cylinders and the toner is deposited onto the media according to the pattern, e.g., the pattern or image is printed on the material. The foregoing process can be adapted to a variety of different print media at speeds of 100 images per minute or faster.  
         [0009]     On the other hand, rub-on image transfers are well-known and include letters and numerals in different type faces which can be transferred from the face of the film on to the target surface (e.g. a drawing on paper) by placing the image face against the paper and rubbing down or burnishing the back of the film so that the letter or numeral becomes attached to the target surface and detached from the film.  
         [0010]     There have been several attempts to extend the digital printing process as described above to transfers, though such attempts have involved more or less complicated procedures and the use of particular materials with limitations as to the nature of the final target surface.  
         [0011]     U.S. Pat. No. 6,656,306 to Mabbott issued Dec. 2, 2003 shows a method for the preparation and application of pressure and heat applied image transfers. An image layer is applied to an image area of an image release surface, and a pressure and/or heat activated adhesive layer is overcoated. The adhesive layer adheres more strongly to the image layer than the image layer does to the release surface, and so with the application of pressure and/or heat, the dried adhesive layer attaches only in the image area to the target surface and the adhesive layer is peeled off except for the image area which is left attached to the target surface.  
         [0012]     It would be greatly advantageous to extend the Mabbott concept to provide a cleaner, clearer more eye-catching graphic.  
       SUMMARY OF THE INVENTION  
       [0013]     It is therefore an object of the present invention to provide a method for the preparation and application of pressure and heat applied image transfers by modifying a large-format digital printer to convert it from heat fused toner printing to cold toner printing, utilizing a very narrow dye range for all coatings, and further making use of the differential thickness between the areas of a release layer where there is toner present and where there is no toner such that adhesive applied to the release layer over the image adheres more strongly to the image than the image does to the release layer. Thus, when transferred to a target surface with the application of pressure and/or heat, the dried adhesive layer attaches only in the image area to the target surface and the adhesive layer is peeled off except for the image area which is left attached to the target surface. This produces a high-resolution four color graphic with white: a cleaner, clearer more eye-catching graphic than previously possible.  
         [0014]     In accordance with the foregoing objects, the present invention is a method for creating and transferring digitally created images on a film to a target surface via heat and/or pressure transfer using a modified large-format digital printer. The method generally comprises the steps of modifying a digital printer to convert it from a front and back heat fused toner printer, to a back fuser toner printer, preparing a transfer film, creating a digital image, applying a release layer onto the transfer film, printing the image onto the release layer on the transfer film in a reverse mirror-image manner, applying an adhesive overtop said image, heat and/or pressure transferring the image onto the target substrate and peeling away the transfer film to selectively leave the image on the target substrate. The present method results in a cleaner, clearer more eye-catching graphic deposited in a more robust, wear-tolerant manner on a wider variety of substrates including rough and porous materials such as leather. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which:  
         [0016]      FIG. 1  is an exploded diagram showing the layers of an exemplary image transfer  2  according to the present invention.  
         [0017]      FIG. 2  is a block diagram of the process steps for making and applying the above-described transfer  2 .  
         [0018]      FIG. 3  is a diagram of the components of an exemplary Xeikon digital printer that are removed as per the necessary modification of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The present invention is a digitally-printed transfer bearing a digitally created image that can be heat and/or pressure-applied to a target surface, and a method for transferring the digitally created images from film to a target surface via digital printing and heat and/or pressure transfer.  
         [0020]     The process employs a modified digital printer (converted from a double sided fusing printing process to a back fusing web printing process) to create an image on transfer film subsequently coated with adhesive that is then heat and/or pressure-applied to a substrate to yield a high-resolution four color graphic with white.  
         [0021]     The basic fabrication steps comprise 1) coating one side of a disposable base transfer film (or carrier) with a releasable coating; 2) digitally printing one or more images overtop the base transfer film in reverse-image format; and 3) applying an adhesive coating over the image.  
         [0022]     The result is a roll of pre-printed transfers. In accordance with the present method for transferring the digitally created images from film to a target surface, 4) the base transfer film is indexed over a target substrate (image down and showing through the film) and heat and/or pressure is applied to the base transfer film to adhere the image to the target substrate. The base transfer film is peeled from the target substrate and is discarded, leaving a high-resolution color graphic image on the target substrate.  
         [0023]     The method is described in detail below with various options, and in all cases the method is unique because when the image is transferred there is “selective release”, meaning that there is transfer to the target substrate only in a pre-determined area (most commonly in the specific area of the print image, though for some applications it may be desirable to have a release that includes non-imaged areas), despite the adhesive coating which may, and indeed, usually exceeds the borders of the printed image. This selective release improves the quality of the transfer because there are no unsightly borders or margins around the image, and holes and gaps in fairly complex images are not filled in.  
         [0024]      FIG. 1  is an exploded diagram showing the layers of an exemplary image transfer  2  according to the present invention. The image transfer  2  includes a disposable base transfer film  11 . This can be any suitable transfer carrier formed of plastic or non-woven material and that is capable of being passed as a web through the production machinery. For example, the presently preferred transfer film  11  is polyester teraphthlate (PET). In accordance with one optional feature of the present invention, the transfer film  11  may be preformed with distinct surface patterns or texture to give the final transfer a textured aesthetic.  
         [0025]     An image release layer  12  is uniformly applied onto the base transfer film  1   1 . Image release layer  12  may be, for example, a wax, lacquer, or combination of wax and lacquer, with or without specific additives. The application of the image release layer  12  may be attained by applying the wax and/or lacquer onto the base transfer film  11  in individual coats from either solvent or waterborne solutions or suspensions. It is known from experience that the final parameters of the coating can be adapted to any requirement by the changing coating weights, the addition or substitution of resins, waxes and wax solutions, and there are many conventional coating methods that can be used to achieving a desired coat weight. The appearance of the final coating can be full gloss or be matted down to the required level by the addition of matting agents. When applied the release layer  12  must be uniform, and free from all coating defects and application patterns (except where a coating pattern is an intended aspect). The presently-preferred release layer  12  comprises a lacquer mixture of commercially available polymethyl methacrylate resin with a commercially available wax suspension (BYK 151 ex-Samual Banner). The ratio of resin to wax is on the order of 80% to 95% resin to 5% to 20% wax. These two components are provided in a 5% to 15% solid solution (depending on method of application) in a butanone and toluene solvent blend (of which toluene is around 10% of the total solvent). The release layer coating is then forced air-dried giving a dry coat weight coat weight of 1.15 to 1.35 grams per square meter.  
         [0026]     The image  13  itself is then digitally printed with a four color graphic (as will be described) on the transfer film  11  (overtop release layer  12 ). The digital printer may employ either electro-ink or dry powder toner, and otherwise conventional print techniques. Preferably, a registration mark is printed at this same time, and when desired the four-color image  13  (and registration mark) is then overprinted with a white background  14 .  
         [0027]     Finally, a pressure and/or heat activated adhesive layer  15  may be applied evenly over the whole of the web, both where there is image and no image, or may be selectively applied only in the image area. Presently, the adhesive layer  15  is applied in line directly after the printing step using a 3.5% to 4% solution of commercially available polyamide (Lioseal V 7036 ex-Henkel) in a solvent system, which is predominately Isopropyl alcohol. This solution is then coated onto the image  13  and/or transfer film  11  by a wire wound rod at a dry coating weight of 0.2 to 0.3 grams per square meter, the applied coating being forced air-dried.  
         [0028]     To then transfer the digitally created image from the transfer film  11  to a target surface, the base transfer film  11  is placed on a target substrate and is indexed in position using the index lines (image down and showing through the film). The adhesive layer is then heat and/or pressure-fused to a subject material and the image itself  13  adheres more strongly to the material than does the image release layer  12 . Thus, when the image transfer film  11  is applied image-down to a target substrate by application of pressure and/or heat (as will be described), the dried adhesive layer  15  attaches to the target substrate only in the image  12  area but is otherwise retained by the transfer film  11  (“selective release”). To then apply the transfer  2 , the image transfer film  11  is peeled off the target substrate together with the dried adhesive layer  15  except for the image area which is left attached to the target substrate by the pressure and/or heat activated adhesive layer  15 . For this to happen, the thickness of the non-printed areas of release layer  12  and adhesive layer  15  must be thinner than printed areas containing the release layer  12 , image  13  and adhesive layer  15  such that more pressure is exerted where there is image to the target substrate than where there is no image. The characteristics of the image release layer  12 , the adhesive layer  15  and the image layers  13 ,  14  are selected so as to work with a wide variety of target substrates, including textured and porous materials such as leather to give this selectivity.  
         [0029]      FIG. 2  is a block diagram of all necessary process steps for making and applying the above-described transfer  2 .  
         [0030]     Step  1 : Modify Digital Printer  
         [0031]     This printer can be any conventional digital printer that uses either ElectroInk™ or dry powder toner, or other conventional print techniques. For example, a Xeikon™ large format digital printer is suitable. This and most other large format digital printers employ heater roller assemblies and fusers generally contained within a protective housing. A toner image is transferred to a sheet or web and is then fixed to the web by heat and/or pressure. Typically the paper is transported in a nip between the fuser and pressure roller, which are rotating. Thermal radiation from a lamp heats the fuser roller, causing the toner on the web to melt and press into the web fibers. In accordance with the present invention, the printer is modified to essentially convert it from a front and back fuser system to a back fusing web printing process. The modification initially entails disabling the heaters in the infeed module removal of the front fusers (substep  22 ) and removal of the GEM rollers  24 . Specifically, for a Xeikon digital printer, the front fusers and part nos. CNS-1262-01 5208 32D (Gem Roller) would be removed as seen in  FIG. 3 . In addition, the print color order is changed from the conventional CMYK to KMCY  
         [0032]     Step  2 : Prepare Web  
         [0033]     The current process uses a plastic web in roll form for the base transfer film  11  of  FIG. 1  and pre-coats this with the release layer  12  which may be a releasing lacquer, a wax, a release coating, or a combination of any of these as described above. At substep  42  it is necessary to mix the releasing layer (lacquer, wax, coating, or combination of any of these). The lacquer, wax and release coating are custom-mixed to create the correct release factor for a range of heat and pressure used. A suitable wax release can be mixed with a combined acrylic nitrocellulose overlacquer for this purpose.  
         [0034]     If desired, the release layer  12  may be texturized or mixed with specific additives, such as UV absorbers or biocides, to give the release layer specific properties.  
         [0035]     For example, the release layer  12  may be texturized with a distinct carrier surface pattern (matte or scratch). Since the image is printed onto the release layer  12  and is then transferred, the net effect is to impart the surface pattern onto the surface of the transfer. Most any texture or pattern that can be made to the surface of the release layer  12 , for example, embossing, etching or addition of a solid component, e.g. silica. In each case this is transferred when it is applied to the target substrate. These changes can be aesthetic for example, matte, brushed effect, geometric pattern, regular pattern or random pattern. The effect can also be subtle such as wording, images or patterns that are only visible with light shining on the surface at a particular angle, thereby serving as a simple security device.  
         [0036]     As another example, the release layer  12  may contain a functional additive that confers a property to the transfer  2  that is not present in the transfer without the additive. For example the addition of 1% of an anti-microbial additive such the transfer surface as applied to a target will inhibit bacteria. Inorganic, silver-based antimicrobials are generally recognized as safe and are well suited for this purpose.  
         [0037]     The addition of a small percentage (less than 10%) of a UV absorber will protect the toner image from degradation in color intensity due to prolonged exposure to direct sunlight.  
         [0038]     The addition of a phosphorescent or fluorescent additive will make the transfer “glow” when UV light is shined onto it. This addition can be used in conjunction with the above-described surface pattern, making the effect easier to detect.  
         [0039]     Step  3 : Prepare Image  
         [0040]     The image is designed into a vector image file, or scanned into a raster image file, in both cases using four color CMYK pixilation.  
         [0041]     As seen at substep  32 , the emblem graphic design may be generated using computer drawing software. This is generally accomplished using graphics programs such as well-known Adobe Illustrator™, Photoshop™, etc. Such software is capable of calculating the image dimensions from the design, and colors are chosen from a selectable palette. Photoshop software developed by Adobe uses a palette technique in which the image data is coded and compressed to a prescribed number of colors (a range of from 256 to 16M colors depending on the selected palette). The image file can be manipulated as desired to resize/rescale, redraw or alter the coloration. The final image is then saved as a CMYK raster image file.  
         [0042]     Step  4 : Print Image  
         [0043]     Given a prepared image, at substep  44  the image is printed directly from the raster image file and at substep  46  an additional toner drum of white toner (W) is used to print a white overprint. The process imprints electrostatically charged toner or inkjet images onto the base transfer film  11 . The process prints the desired image, laying on colors in registration patterns in the order Black, Magenta, Cyan, Yellow (KMCY), and finally White, instead of the CMYK patterns that are applied by an unmodified Xeikon. The printing of a white layer of color at substep  66  is unique to the invention and this improves contrast by filling in blank areas. When working on the design computer white is seen as black. White cannot be seen on the screen. The black image (the part we want to be white) is given a specific reference, for example, pantone  100 . This specific reference number is added as a 5 th  color that the Xeikon combines with the normal CMYK colors of the design, and yet printing this reference color as white as it has been programmed to do.  
         [0044]     Step  5 : Apply Release Layer  
         [0045]     Next, at step  5 , the mixed release layer  12  is applied to the plastic transfer film  11 . The release layer  12  is applied over the whole surface of the base transfer film  11  using conventional coating machine.  
         [0046]     Step  6 : Apply Adhesive  
         [0047]     At step  6  a water or solvent based adhesive is applied over both the image (with nor without white) and the areas that do not contain a printed image. These areas may include parts of the image that have intentionally been left clear of print for example between numbers, backgrounds to let the substrate be seen through the print, etc. The transfer  2  is now complete.  
         [0048]     Step  7 : Apply finished Transfer  2   
         [0049]     Finally, at step  7 , the image transfer  2  may be applied to a wide variety of materials including rough and/or porous materials such as leather. At substep  72  the image  13  may be transferred to the substrate material by a roller-to-substrate process, or through a heat-stamping process, in both cases using conventional presses. In both cases the differential pressure of the transfer film  11  with toner versus the transfer film  11  without toner is the factor that controls the selective release according to the present invention. More specifically, at substep  74  the dried adhesive on the printed area of the image  13  encounters more pressure due to the additional thickness added by the toner, and thus the printed areas of image  13  attach to the target material. After the transfer film  11  contacts the target substrate, the transfer film  11  may be peeled away. The printed image  13  transfers to the target substrate as the web separates. The adhesive on the printed area attaches to the target surface and pulls the printed image off the transfer film  11  and onto the target substrate. The process does not leave a “lacquer halo” around the printed images as in conventional transfer processes.  
         [0050]     Where a heat-stamping process is used, the stamping press may be used a second time directly onto the transferred image to imbed the printed image into the selected substrate.  
         [0051]     This differential pressure is obtained by the difference in thickness between the areas of the film that are imprinted with the image  13  and areas where there is no image. Although it is imperceptible to the naked eye, the transfer  2  is thicker in the areas where the toner has been applied. The image is transferred selectively through the interaction of the release layer, image and adhesive and the target substrate. The release layer and adhesives being specifically formulated to exploit this differential pressure.  
         [0052]     Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications thereto may obviously occur to those skilled in the art upon becoming familiar with the underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth herein.